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Matter and its States PYQs – Chemistry, SSC & Railway

80 Matter and its States (Chemistry) questions asked in recent SSC and Railway exams, newest first, with exam, date & shift, answers and solutions.

📚 80 questionsSSC 15 · Railway 65
RRB Group D 2025-26 – 12 August 2026 Shift 3 · Physical and chemical changes

Q1. Which of the following is a chemical change and NOT a physical change?

  1. (a) Rusting of iron
  2. (b) Melting of ice
  3. (c) Dissolving sugar in water
  4. (d) Boiling of water
Answer & solution

Answer: (a) Rusting of iron

Answer: Option 1 – Rusting of iron.
•Rustingforms a new substance (iron oxide) ⇒ chemical change. Melting, dissolving and boiling are physical.
RRB Group D 2025-26 – 11 August 2026 Shift 2 · Physical and chemical changes

Q2. In a solution, which observation suggests a chemical change has taken place?

  1. (a) Dissolving of solid
  2. (b) Formation of a precipitate
  3. (c) Uniform mixing of substances
  4. (d) Increase in temperature only
Answer & solution

Answer: (b) Formation of a precipitate

Answer: Option 2 – Formation of a precipitate.
• A new insoluble solid (precipitate) indicates a new substance has formed – i.e. a chemical change.
RRB Group D 2025-26 – 9 August 2026 Shift 3 · Physical and chemical changes

Q3. Which statement is correct regarding physical and chemical changes?

  1. (a) All physical changes are irreversible
  2. (b) Chemical changes alter composition
  3. (c) All changes in solutions are chemical
  4. (d) Physical changes form new substances
Answer & solution

Answer: (b) Chemical changes alter composition

Answer: Option 2 — Chemical changes alter composition
A chemical changealters the compositionand forms new substances → Option 2.
RRB Group D 2025-26 – 4 August 2026 Shift 2 · Physical and chemical changes

Q4. Which statement correctly shows that a chemical change is different from a physical change?

  1. (a) Chemical change affects only size and shape, while physical change affects composition.
  2. (b) Chemical change is always reversible, while physical change is never reversible.
  3. (c) Chemical change results in a new substance, while physical change does not.
  4. (d) Chemical change changes only appearance, while physical change forms new substances.
Answer & solution

Answer: (c) Chemical change results in a new substance, while physical change does not.

Answer: Option 3 — Chemical change results in a new substance, physical change does not
Achemical change forms a new substance; a physical change alters only state/appearance → Option 3.
RRB NTPC UG CBT-1 2025-26 – 16 June 2026 Shift 1 · Physical and chemical changes

Q5. Which of the following is a physical change only?

  1. (a) Crystallization
  2. (b) Combustion
  3. (c) Oxidation
  4. (d) Reduction
Answer & solution

Answer: (a) Crystallization

Physical vs Chemical Change
Physical Change:No new substance formed, reversible
Chemical Change:New substance formed, irreversible
Crystallization:Solid crystals form from solution
Only state changes, composition remains same
Example: Salt crystals from salt water
Combustion, Oxidation, Reduction:All chemical changes
New substances formed with different properties
Answer: Option 1 → Crystallization
RRB NTPC UG CBT-1 2025-26 – 14 June 2026 Shift 3 · States of matter and their properties

Q6. Which of the following is a characteristic feature of the gaseous state of matter?

  1. (a) High rigidity and fixed volume
  2. (b) Strong intermolecular forces and fixed shape
  3. (c) Definite volume but no definite shape
  4. (d) Negligible intermolecular forces and high compressibility
Answer & solution

Answer: (d) Negligible intermolecular forces and high compressibility

Topic:States of Matter - Gaseous State
Characteristics of Gases:
• Particles are far apart with negligible intermolecular forces
• No fixed shape or volume - takes shape of container
• Highly compressible due to large intermolecular spaces
• Particles move freely with high kinetic energy
Analysis of Options:
Option 1: Rigidity & fixed volume → Solid property
Option 2: Strong forces & fixed shape → Solid property
Option 3: Definite volume, no shape → Liquid property
Option 4: Negligible forces & high compressibility → Gas ✓
SSC GD 2026 – 29 May 2026 Shift 2 · Evaporation and its factors

Q7. Which of the following statements is NOT correct?

  1. (a) Evaporation causes warming.
  2. (b) States of matter are interconvertible.
  3. (c) Boiling is a bulk property.
  4. (d) Evaporation is a surface phenomenon.
Answer & solution

Answer: (a) Evaporation causes warming.

Correct Answer: Evaporation causes warming — Option (a)
The statement 'Evaporation causes warming' is NOT correct — evaporation actually causes COOLING. About Evaporation and temperature: Evaporation causes COOLING (not warming/heating); Process of evaporation: Molecules at the surface of a liquid gain enough kinetic energy to overcome intermolecular forces and escape into the gaseous phase; The molecules that escape are the HIGH-ENERGY molecules; This leaves behind lower-energy (cooler) molecules in the liquid; The average kinetic energy of the remaining liquid decreases → temperature falls → COOLING effect; This is called 'evaporative cooling'; Latent heat of vaporization: Evaporation absorbs heat from the surroundings (latent heat of vaporization); This absorption of heat causes cooling; Examples of evaporative cooling: Sweating — sweat evaporates and cools the body; Earthen pots ( matkas ) keep water cool through evaporation; Desert coolers (evaporative coolers) work on this principle; Fever reduction by wiping with damp cloth; Evaluation of all statements: Statement (a) — 'Evaporation causes warming' — FALSE/INCORRECT: Evaporation causes COOLING, not warming; Statement (b) — 'States of matter are interconvertible' — TRUE: Matter can change between solid, liquid, and gas states (melting, freezing, vaporization, condensation, sublimation); Statement (c) — 'Boiling is a bulk property' — TRUE: Boiling occurs throughout the liquid (in bulk), not just at the surface; it happens at a fixed temperature (boiling point) at a given pressure; unlike evaporation (surface phenomenon), boiling is a bulk phenomenon; Statement (d) — 'Evaporation is a surface phenomenon' — TRUE: Evaporation occurs only at the surface of the liquid (unlike boiling which occurs throughout); molecules escape from the surface only.
Option (b) States of matter are interconvertible — Incorrect as an answer (statement is TRUE): States of matter ARE interconvertible — solid ↔ liquid (melting/freezing), liquid ↔ gas (vaporization/condensation), solid ↔ gas (sublimation/deposition); these are physical changes; the statement is TRUE and NOT the incorrect one.
Option (c) Boiling is a bulk property — Incorrect as an answer (statement is TRUE): Boiling IS a bulk property/phenomenon — it occurs throughout the liquid at a fixed boiling point; bubbles form throughout the liquid; boiling requires a specific temperature (boiling point) and occurs at a fixed temperature; this distinguishes it from evaporation (surface phenomenon); the statement is TRUE and NOT the incorrect one.
Option (d) Evaporation is a surface phenomenon — Incorrect as an answer (statement is TRUE): Evaporation IS a surface phenomenon — it occurs only at the surface of a liquid; only molecules at the liquid surface with sufficient kinetic energy can escape into the vapor phase; this is why evaporation is a gradual, slow process (unlike boiling); the statement is TRUE and NOT the incorrect one. The candidate incorrectly selected this option.
SSC GD 2026 – 22 May 2026 Shift 1 · Interconversion of states (melting, boiling, sublimation, deposition)

Q8. What is the change of state from liquid to gas at atmospheric pressure called?

  1. (a) Solidification
  2. (b) Deposition
  3. (c) Freezing
  4. (d) Vaporization
Answer & solution

Answer: (d) Vaporization

Correct Answer: Vaporization — Option (d)
The change of state from liquid to gas at atmospheric pressure is called Vaporization ( वाष्पीकरण ). Types of phase changes (state changes): Solid → Liquid: Melting (also called Fusion); Liquid → Solid: Solidification (also called Freezing); Liquid → Gas: Vaporization (evaporation at surface, or boiling throughout); Gas → Liquid: Condensation; Solid → Gas (directly): Sublimation; Gas → Solid (directly): Deposition; About Vaporization: Vaporization occurs in two ways: Evaporation — occurs at the surface of a liquid at any temperature (e.g., water evaporating from a wet cloth); Boiling — occurs throughout the liquid at its boiling point (100°C for water at 1 atm pressure); Both are forms of vaporization; During vaporization: Liquid absorbs latent heat of vaporization (energy needed to break intermolecular bonds); Temperature remains constant during boiling despite continuous heating; Water's latent heat of vaporization: 2260 kJ/kg; Importance: Vaporization is the key process in the water cycle (evaporation from oceans/rivers), sweating (cooling mechanism in humans), steam engines, and refrigeration.
Option (a) Solidification — Incorrect: Solidification is the change of state from LIQUID to SOLID (the reverse of melting); it is NOT the liquid-to-gas change; for example, water solidifies to form ice when temperature drops below 0° C at standard pressure.
Option (b) Deposition — Incorrect: Deposition is the change of state directly from GAS to SOLID (bypassing the liquid phase) — the reverse of sublimation; for example, frost formation on cold surfaces (water vapour directly depositing as ice); it is not the liquid-to-gas change.
Option (c) Freezing — Incorrect: Freezing is the same as Solidification — the change of state from LIQUID to SOLID; for example, water freezing to form ice at 0°C; it is NOT the liquid-to-gas transition which is called Vaporization.
SSC GD 2026 – 21 May 2026 Shift 2 · States of matter and their properties

Q9. When the temperature of a substance increases, what happens to the kinetic energy of its particles?

  1. (a) Decreases
  2. (b) Increases
  3. (c) Remains constant
  4. (d) It converts to potential energy
Answer & solution

Answer: (b) Increases

Correct Answer: Increases — Option (b)
When the temperature of a substance increases, the kinetic energy of its particles increases. Fundamental relationship: Temperature is a measure of the average kinetic energy of the particles (atoms, molecules, ions) of a substance — this is a foundational principle of the Kinetic Theory of Matter; As temperature rises, particles absorb thermal energy and move faster (in gases and liquids) or vibrate more rapidly (in solids); Mathematical relationship: The average kinetic energy (KE) is directly proportional to the absolute temperature: KE = (3/2) kT , where k is the Boltzmann constant and T is the absolute temperature in Kelvin; States of matter implications: In gases: higher temperature → faster molecular motion → more frequent and forceful collisions → higher pressure (at constant volume); In liquids: higher temperature → faster motion → eventually evaporation occurs; In solids: higher temperature → more vigorous vibrations → thermal expansion; Practical applications: Thermometers measure temperature based on expansion due to increased particle kinetic energy; temperature is the macroscopic measure of the microscopic kinetic energy of particles.
Option (a) Decreases — Incorrect: Kinetic energy does NOT decrease when temperature increases — it increases; kinetic energy decreases when temperature falls (cooling); if a substance is cooled to absolute zero (0 Kelvin or -273.15°C), particle motion theoretically stops — this is the minimum kinetic energy state.
Option (c) Remains constant — Incorrect: Kinetic energy does NOT remain constant when temperature changes; by definition, temperature IS the measure of average kinetic energy — if temperature changes, kinetic energy must change; kinetic energy would only remain constant if temperature remained constant.
Option (d) It converts to potential energy — Incorrect: Kinetic energy does not simply convert to potential energy when temperature increases; potential energy (due to intermolecular forces) does change during phase transitions (e.g., melting or boiling) when temperature remains constant and energy goes into overcoming intermolecular forces — but during simple heating (not phase change), kinetic energy increases.
RRB NTPC GL CBT-1 2025-26 – 24 March 2026 Shift 2 · States of matter and their properties

Q10. What property do solids possess due to their closely packed particles?

  1. (a) Compressibility
  2. (b) Transparency
  3. (c) Fluidity
  4. (d) Rigidity
Answer & solution

Answer: (d) Rigidity

Property of Solids
Solids have particles that areclosely packedin a fixed arrangement.
This close packing gives solids adefinite shape and volume.
The particles cannot move freely, making solidsrigid(not easily deformable).
Other options: Compressibility (gases), Fluidity (liquids/gases), Transparency (depends on material).
Answer: Option 4 → Rigidity
RRB NTPC GL CBT-1 2025-26 – 16 March 2026 Shift 3 · States of matter and their properties

Q11. The state of matter where particles are far apart and move randomly and quickly is the:

  1. (a) Solid state
  2. (b) Gaseous state
  3. (c) Liquid state
  4. (d) Plasma state
Answer & solution

Answer: (b) Gaseous state

GASEOUS state: particles far apart, move randomly and quickly,
very weak intermolecular forces.
Comparison of states:
• Solid → tightly packed, definite shape and volume.
• Liquid → moderate spacing, takes shape of container.
• Gas → far apart, no fixed shape or volume, high kinetic energy.
• Plasma → super- energised ionised gas (4th state, e.g., stars, lightning).
Answer: Option 2 → Gaseous state
RRB Technician Grade III 2025-26 – 6 March 2026 Shift 3 · Interconversion of states (melting, boiling, sublimation, deposition)

Q12. At high altitudes such as hill stations, water boils at a temperature lower than 100°C, whereas in a pressure cooker it boils above 100°C. Which of the following statements correctly explains this phenomenon?

  1. (a) Boiling point of a liquid is independent of external pressure and depends only on temperature.
  2. (b) Water molecules at high altitude have lower kinetic energy than at sea level, so they boil at a lower temperature.
  3. (c) Boiling point of a liquid decreases with an increase in atmospheric pressure and increases with a decrease in atmospheric pressure.
  4. (d) Boiling point of a liquid increases with an increase in atmospheric pressure and decreases with a decrease in atmospheric pressure.
Answer & solution

Answer: (d) Boiling point of a liquid increases with an increase in atmospheric pressure and decreases with a decrease in atmospheric pressure.

Boiling point of a liquid is the temperature at which its vapour pressure equals the external pressure.
At high altitudes, atmospheric pressure is lower than at sea level.
Lower pressure means water boils at temperatures below 100°C.
In a pressure cooker, pressure is higher than atmospheric pressure.
Higher pressure raises the boiling point above 100°C.
Hence, boiling point increases with atmospheric pressure increase and decreases with pressure decrease.
Final answer: Option 4
RRB Technician Grade III 2025-26 – 6 March 2026 Shift 3 · Evaporation and its factors

Q13. Read the given statements carefully and select the correct option.
Statement I: The phenomenon of change of liquid into vapours at any temperature below its boiling point is called evaporation.
Statement II: The rate of evaporation increases with an increase of surface area.

  1. (a) Statement I is false but statement II is true.
  2. (b) Both statements I and II are true.
  3. (c) Both statements I and II are false.
  4. (d) Statement I is true but statement II is false.
Answer & solution

Answer: (b) Both statements I and II are true.

Statement I is true because evaporation is the process of liquid changing into vapour below its boiling point.
Statement II is true since increasing the surface area allows more molecules to escape, raising the evaporation rate.
Thus, both statements are correct.
Final answer: Option 2
RRB JE CBT-1 2025-26 – 25 February 2026 Shift 3 · States of matter and their properties

Q14. What conclusion can be drawn from the experiment in which potassium permanganate solution remains coloured even after repeated dilution?

  1. (a) Particles of matter are fixed and stationary
  2. (b) Particles of matter occupy no space at all
  3. (c) Particles of matter are visible to naked eye
  4. (d) Particles of matter are extremely small in size
Answer & solution

Answer: (d) Particles of matter are extremely small in size

The potassium permanganate solution remains coloured even after repeated dilution.
This shows that the particles causing colour are very small but still present in the solution.
Hence, the particles of matter must be extremely small in size, allowing the colour to persist despite dilution.
Larger particles would have disappeared or settled out after dilution.
Therefore, the correct conclusion is that particles are extremely small in size.
Final answer: Option 4
RRB JE CBT-1 2025-26 – 25 February 2026 Shift 3 · Evaporation and its factors

Q15. Why does our palm feel cold when acetone or petrol is poured on it?

  1. (a) The liquid increases moisture on skin surface
  2. (b) The liquid reacts chemically with our skin surface
  3. (c) The liquid blocks heat flow from surroundings
  4. (d) The liquid absorbs heat from the skin to evaporate
Answer & solution

Answer: (d) The liquid absorbs heat from the skin to evaporate

The palm feels cold because acetone or petrol evaporates quickly.
Evaporation requires heat energy, which is taken from the skin’s surface.
This heat absorption reduces skin temperature, causing a cool sensation.
Hence, the liquid absorbs heat from the skin to evaporate, making it feel cold.
Final answer: Option 4
SSC MTS 2025 – 20 February 2026 Shift 1 · Interconversion of states (melting, boiling, sublimation, deposition)

Q16. What is the change of state directly from solid to gas without changing into liquid state known as?

  1. (a) Solidification
  2. (b) Sublimation
  3. (c) Freezing
  4. (d) Evaporation
Answer & solution

Answer: (b) Sublimation

Correct Answer: Sublimation (Option 2)
Sublimation is the process in which a solid directly converts into a gas ( vapour ) without passing through the liquid phase. Examples include: dry ice (solid CO₂), iodine crystals, camphor, naphthalene balls.
Why other options are wrong:
Option 1 – Solidification (also called freezing) is the change from liquid to solid.
Option 3 – Freezing is the change from liquid to solid, not solid to gas.
Option 4 – Evaporation is the change from liquid to gas at the surface, not solid to gas.
RRB JE CBT-1 2025-26 – 20 February 2026 Shift 2 · States of matter and their properties

Q17. Which of the following best supports the concept that matter is made-up of particles?

  1. (a) A drop of ink spreads uniformly in water
  2. (b) Water boils at 100°C
  3. (c) Ice melts to form water
  4. (d) Metals conduct electricity
Answer & solution

Answer: (a) A drop of ink spreads uniformly in water

Option 1 is correct: A drop of ink spreads uniformly in water.
This shows that matter is made up of tiny particles which move and mix with each other.
The spreading happens because the particles of ink and water move and mix at the microscopic level.
Other options describe physical properties but do not directly demonstrate the particle nature of matter.
Hence, the concept that matter is made of particles is best supported by the uniform spreading of ink in water.
Final answer: Option 1
RRB JE CBT-1 2025-26 – 20 February 2026 Shift 2 · Diffusion

Q18. Which of the following will diffuse slowest in air?

  1. (a) Oxygen
  2. (b) Chlorine
  3. (c) Ammonia
  4. (d) Hydrogen
Answer & solution

Answer: (b) Chlorine

Diffusion rate is inversely proportional to the square root of molar mass (Graham's law).
Molar masses: Oxygen (32 g/mol), Chlorine (around 71 g/mol), Ammonia (17 g/mol), Hydrogen (2 g/mol).
Chlorine has the highest molar mass among these gases.
Therefore, chlorine diffuses slowest in air due to its greater molar mass.
Answer is Option 2.
RRB JE CBT-1 2025-26 – 20 February 2026 Shift 2 · States of matter and their properties

Q19. Which property correctly distinguishes liquids from solids?

  1. (a) Liquids have fixed shape but no fixed volume
  2. (b) Liquids have fixed volume but no fixed shape
  3. (c) Liquids are completely incompressible in nature
  4. (d) Liquids cannot diffuse into other substances
Answer & solution

Answer: (b) Liquids have fixed volume but no fixed shape

Option 2 is correct.
Liquids have a fixed volume but no fixed shape.
This means they take the shape of the container they are in, unlike solids which have fixed shape and volume.
Liquids are not completely incompressible, and they can diffuse, so options 3 and 4 are incorrect.
Option 1 is also wrong because liquids don't have a fixed shape.
Hence, the key property that distinguishes liquids from solids is that liquids have fixed volume but no fixed shape.
Answer ends here.
RRB JE CBT-1 2025-26 – 20 February 2026 Shift 1 · States of matter and their properties

Q20. Why are solids described as rigid in nature?

  1. (a) Their particles possess very low mass and volume
  2. (b) Their particles are closely packed with strong attraction
  3. (c) Their particles slide easily under applied external force
  4. (d) Their particles move freely with weak mutual attraction
Answer & solution

Answer: (b) Their particles are closely packed with strong attraction

Solids are called rigid because their particles are very closely packed.
This close packing results in strong attractive forces between particles.
Strong attraction keeps the particles fixed in position, limiting movement.
Due to this, solids maintain a definite shape and resist deformation.
Hence, solids appear rigid under external forces.
Final answer: Option 2
RRB JE CBT-1 2025-26 – 20 February 2026 Shift 2 · States of matter and their properties

Q21. Why do gases exert pressure on the walls of the container?

  1. (a) Gas particles attract the container walls strongly
  2. (b) Gas particles move randomly and strike the walls
  3. (c) Gas particles stay fixed inside the container
  4. (d) Gas particles possess very low kinetic energy
Answer & solution

Answer: (b) Gas particles move randomly and strike the walls

Correct Option: 2
Gases consist of particles moving randomly in all directions.
These particles collide with the walls of the container.
Each collision exerts a force on the wall.
The continuous collisions of gas particles cause pressure on the container walls.
Thus, gas pressure originates from particles striking the walls due to their random motion.
This explains why gases exert pressure on container walls.
RRB JE CBT-1 2025-26 – 20 February 2026 Shift 2 · Evaporation and its factors

Q22. Why do wet clothes dry faster when spread out?

  1. (a) Clothes become hotter
  2. (b) Water escapes faster due to sunlight
  3. (c) Water boils off
  4. (d) Surface area is increased
Answer & solution

Answer: (d) Surface area is increased

Correct option is 4
Wet clothes dry because water evaporates from them.
When clothes are spread out, their surface area increases.
More surface area allows more water molecules to evaporate at the same time.
This speeds up the drying process.
Hence, wet clothes dry faster when spread out due to increased surface area.
This is a simple principle of evaporation rate and surface exposure.
Answer is option 4.
End of answer.
RRB JE CBT-1 2025-26 – 19 February 2026 Shift 3 · States of matter and their properties

Q23. Which measurable quantity remains the same when a liquid is transferred between containers?

  1. (a) Mass of the liquid becomes zero
  2. (b) Density of the liquid always increases
  3. (c) Volume of the liquid remains unchanged
  4. (d) Shape of the liquid remains unchanged
Answer & solution

Answer: (c) Volume of the liquid remains unchanged

The volume of a liquid is a measure of the space it occupies.
When transferring a liquid from one container to another, no liquid is lost, so its volume remains the same.
Mass may remain same but does not become zero; density can change with temperature; shape changes according to container.
Hence, the measurable quantity that remains unchanged is the volume of the liquid.
Final answer: Option 3
SSC MTS 2025 – 11 February 2026 Shift 2 · States of matter and their properties

Q24. Which of the following is a characteristic of liquids?

  1. (a) Fixed shape and fixed volume
  2. (b) No fixed shape but fixed volume
  3. (c) Fixed shape but no fixed volume
  4. (d) No fixed shape and no fixed volume
Answer & solution

Answer: (b) No fixed shape but fixed volume

The correct answer is No fixed shape but fixed volume (Option 2). Liquids do not have a fixed shape — they take the shape of the container they are placed in. However, they do have a fixed (definite) volume because the intermolecular forces in liquids are strong enough to hold the molecules together. Option 1 (Fixed shape and fixed volume) describes solids. Option 3 is incorrect. Option 4 (No fixed shape and no fixed volume) describes gases.
SSC MTS 2025 – 5 February 2026 Shift 1 · Interconversion of states (melting, boiling, sublimation, deposition)

Q25. What is the minimum temperature at which a solid melts to become liquid at the atmospheric pressure known as?

  1. (a) Boiling point
  2. (b) Melting point
  3. (c) Absolute point
  4. (d) Vaporization point
Answer & solution

Answer: (b) Melting point

Correct Answer: Melting point
The Melting Point is the minimum temperature at which a solid changes to liquid state at standard atmospheric pressure. At this temperature, the solid and liquid phases exist in equilibrium. For example, the melting point of ice is 0 degrees Celsius.
Why other options are wrong:
Boiling point - The temperature at which a liquid changes to vapour /gas state.
Absolute point - Not a standard scientific term for this concept.
Vaporization point - Another term for boiling point; not for solid-to-liquid transition.
Delhi Police Constable (Exe) 2025-26 – 18 December 2025 Shift 1 · States of matter and their properties

Q26. In which state of matter are the molecules closely packed together and maintain a fixed shape?

  1. (a) Gas
  2. (b) Liquid
  3. (c) Solid
  4. (d) Plasma
Answer & solution

Answer: (c) Solid

In the solid state of matter, molecules are closely packed together in a fixed, ordered arrangement. Solids have a definite shape and a definite volume. The intermolecular forces in solids are very strong, which is why solids maintain their shape without needing a container.
Option (a) is incorrect: In gases, molecules are far apart, move randomly, and have no fixed shape or volume.
Option (b) is incorrect: In liquids, molecules are close but can move past each other, so liquids have no fixed shape (they take the shape of the container) but do have a fixed volume.
Option (d) is incorrect: Plasma is a high-energy state consisting of ionized particles; it has no fixed shape or structure and is sometimes called the fourth state of matter.
SSC CHSL Tier-1 2025 – 24 November 2025 Shift 1 · Interconversion of states (melting, boiling, sublimation, deposition)

Q27. What is the change of state directly from gas to solid without changing into liquid state known as?

  1. (a) Solidification
  2. (b) Deposition
  3. (c) Freezing
  4. (d) Evaporation
Answer & solution

Answer: (b) Deposition

Correct Answer: Deposition (Option 2)
Deposition (also called desublimation or anti-sublimation) is the direct change of state from gas to solid, bypassing the liquid state. Example: water vapour directly forming frost (ice crystals) on cold surfaces. The reverse process (solid to gas directly) is called Sublimation.
Solidification is the change from liquid to solid (e.g., water freezing to ice), not gas to solid.
Freezing also refers to the liquid-to-solid transition — it is not a gas-to-solid process.
Evaporation is the change from liquid to gas (the opposite direction), not gas to solid.
SSC CHSL Tier-1 2025 – 21 November 2025 Shift 1 · Interconversion of states (melting, boiling, sublimation, deposition)

Q28. What happens to solid carbon dioxide (dry ice) when the pressure is decreased to 1 atmosphere?

  1. (a) It sublimates directly into a gas.
  2. (b) It melts into a liquid.
  3. (c) It remains as a solid.
  4. (d) It freezes further into a solid.
Answer & solution

Answer: (a) It sublimates directly into a gas.

Solid carbon dioxide (dry ice) sublimates directly into a gas (CO2) when the pressure is decreased to 1 atmosphere (standard atmospheric pressure). This is because the triple point of CO2 is at 5.1 atm. At pressures below 5.1 atm, CO2 cannot exist as a liquid — it transitions directly from solid to gas (sublimation). This property makes dry ice useful for cooling without creating liquid. Why other options are wrong: Option 2 - Melts into liquid: CO2 can only become liquid at pressures above 5.1 atm; at 1 atm it sublimates. Option 3 - Remains solid: At 1 atm and above -78.5°C, dry ice will sublimate, not remain solid. Option 4 - Freezes further: Reducing pressure does not cause dry ice to freeze further; it sublimates.
SSC CHSL Tier-1 2025 – 20 November 2025 Shift 1 · States of matter and their properties

Q29. The forces of attraction between the particles are maximum in _____ and minimum in _____.

  1. (a) solids, gases
  2. (b) gases, liquid
  3. (c) solids, liquid
  4. (d) gases, solids
Answer & solution

Answer: (a) solids, gases

In solids, particles are very closely packed and the intermolecular forces of attraction are maximum. In gases, particles are far apart from each other, so the forces of attraction between particles are minimum. This explains why solids have a definite shape and volume, while gases have neither. Why other options are wrong: Option 2 (gases, liquid): Incorrect; gases have minimum forces of attraction, and liquids have intermediate forces. Option 3 (solids, liquid): Solids have maximum forces, but liquids do not have minimum forces — gases have minimum forces. Option 4 (gases, solids): Completely reversed; solids have maximum attraction, not gases.
SSC CHSL Tier-1 2025 – 20 November 2025 Shift 2 · States of matter and their properties

Q30. Which of the following statement is correct regarding gaseous state?
I. In this state, the particles move about randomly at high speed
II. Gases are highly compressible

  1. (a) Only I
  2. (b) Only II
  3. (c) Both I and II
  4. (d) Neither I nor II
Answer & solution

Answer: (c) Both I and II

Correct Answer: Both I and II (Option 3)
Both statements about gaseous state are correct.
Statement I is correct: In a gaseous state, particles (atoms or molecules) have very high kinetic energy and move randomly at high speed in all directions due to negligible intermolecular forces.
Statement II is correct: Gases are highly compressible because there is a large amount of empty space between gas molecules, which can be reduced by applying pressure.
Hence, both I and II are correct.
SSC CHSL Tier-1 2025 – 19 November 2025 Shift 3 · Interconversion of states (melting, boiling, sublimation, deposition)

Q31. Which of the following statements about the state of substances is correct?

  1. (a) Pressure alone determines whether a substance is a solid, liquid, or gas.
  2. (b) Temperature alone determines the state of a substance.
  3. (c) Both pressure and temperature influence the state of a substance.
  4. (d) State changes are unaffected by pressure and temperature.
Answer & solution

Answer: (c) Both pressure and temperature influence the state of a substance.

Correct Answer: Both pressure and temperature influence the state of a substance.
The state of matter (solid, liquid, or gas) is determined by both temperature AND pressure. This is illustrated by the phase diagram of a substance, which shows the conditions of temperature and pressure at which different phases exist. For example:
- Water boils at 100°C at 1 atm pressure, but at lower temperatures at reduced pressure (e.g., on mountains).
- Increasing pressure on ice can cause it to melt (regelation).
- Gases can be liquefied by increasing pressure and/or reducing temperature.
Why other options are wrong:
- Pressure alone: Both factors matter, not just pressure.
- Temperature alone: Both factors matter, not just temperature.
- Unaffected by both: Both temperature and pressure do affect the state of matter.
SSC CHSL Tier-1 2025 – 13 November 2025 Shift 1 · Interconversion of states (melting, boiling, sublimation, deposition)

Q32. What is the change of state from liquid to solid at atmospheric pressure known as?

  1. (a) Solidification
  2. (b) Deposition
  3. (c) Sublimation
  4. (d) Evaporation
Answer & solution

Answer: (a) Solidification

Correct Answer: Solidification
Solidification (also called freezing) is the process by which a substance changes from the liquid state to the solid state when its temperature is lowered to its freezing point at atmospheric pressure. Example: Water freezing to form ice at 0 degrees C.
Why other options are wrong:
- Deposition: Change of state directly from gas to solid (e.g., frost formation), skipping the liquid phase.
- Sublimation: Change of state directly from solid to gas (e.g., dry ice/camphor), skipping the liquid phase.
- Evaporation: Change of state from liquid to gas at the surface of a liquid.
SSC CHSL Tier-1 2025 – 12 November 2025 Shift 2 · Evaporation and its factors

Q33. Which of the following is NOT a main factor affecting the rate of evaporation?

  1. (a) Surface area
  2. (b) Buoyancy
  3. (c) Wind speed
  4. (d) Humidity
Answer & solution

Answer: (b) Buoyancy

Buoyancy is an upward force exerted by a fluid on an object submerged in it — it has no relation to the rate of evaporation. The main factors affecting evaporation are: surface area (larger surface = faster evaporation), wind speed (higher wind = faster evaporation), temperature, and humidity (lower humidity = faster evaporation).
SSC CHSL Tier-1 2025 – 12 November 2025 Shift 2 · Evaporation and its factors

Q34. Which of the following is NOT a main factor affecting the rate of evaporation?

  1. (a) Surface area
  2. (b) Buoyancy
  3. (c) Wind speed
  4. (d) Humidity
Answer & solution

Answer: (b) Buoyancy

Correct Answer: Buoyancy
Buoyancy is the upward force exerted by a fluid on an object submerged in it (Archimedes' Principle). It has no direct relationship with the rate of evaporation.
The main factors that DO affect evaporation rate are:
- Surface area: Larger area = more evaporation.
- Wind speed: Higher wind disperses water vapour , increasing evaporation.
- Humidity: Lower humidity = faster evaporation.
- Temperature: Higher temperature = higher evaporation rate.
RRB NTPC UG CBT-1 2024-25 – 13 August 2025 Shift 3 · Plasma and Bose-Einstein condensate

Q35. In 1995, physicists Eric Cornell and Carl Wieman created the first Bose-Einstein condensate (BEC) using which isotope?

  1. (a) Sodium-23
  2. (b) Thorium-232
  3. (c) Rubidium-87
  4. (d) Caesium-133
Answer & solution

Answer: (c) Rubidium-87

RRB NTPC GL CBT-1 2024-25 – 21 June 2025 Shift 2 · States of matter and their properties

Q36. Let’s denote Z as the number of atoms per unit cell, M as the molar mass of the substance, and Nₐ as Avogadro’s number. Which formula is used to calculate the density (d) of a unit cell?

  1. (a) d = (a³ × Nₐ) / (Z × M)
  2. (b) d = (Z × Nₐ) / (M × a³)
  3. (c) d = (M × a³) / (Z × Nₐ)
  4. (d) d = (Z × M) / (a³ × Nₐ)
Answer & solution

Answer: (d) d = (Z × M) / (a³ × Nₐ)

RRB NTPC GL CBT-1 2024-25 – 20 June 2025 Shift 3 · States of matter and their properties

Q37. The coordination number of atoms in a body-centered cubic (BCC) lattice is:

  1. (a) 8
  2. (b) 12
  3. (c) 4
  4. (d) 6
Answer & solution

Answer: (a) 8

RRB NTPC GL CBT-1 2024-25 – 5 June 2025 Shift 1 · Physical and chemical changes

Q38. Which of the following is an example of a chemical change?

  1. (a) Cutting paper
  2. (b) Melting ice
  3. (c) Boiling water
  4. (d) Burning wood
Answer & solution

Answer: (d) Burning wood

RRB Technician Grade III 2024-25 – 30 December 2024 Shift 1 · Evaporation and its factors

Q39. Which of the following factors does NOT affect the rate of evaporation?

  1. (a) Surface area of the liquid
  2. (b) Temperature of the liquid
  3. (c) Colour of the liquid
  4. (d) Humidity of the surrounding air
Answer & solution

Answer: (c) Colour of the liquid

Correct Answer: Option 3 — Colour of the liquid
Evaporation is the change of a liquid into vapour from its surface alone, at any temperature below the boiling point. It occurs because a few surface particles always possess more than the average kinetic energy and break free from the attraction of their neighbours.
Everything that decides how many particles escape therefore controls the rate — surface area, temperature, humidity and wind speed. The colour of the liquid is only an optical property; it changes nothing about the particles' kinetic energy or about the forces holding them together, so it does not affect the rate of evaporation. (Colour can matter only indirectly, when a dark liquid absorbs more sunlight and so gets hotter — the real factor is still the temperature.)
❌ Why the other options are incorrect
✗ Surface area of the liquid — evaporation is a surface phenomenon; a larger exposed surface lets more particles escape, which is why wet clothes are spread out to dry.
✗ Temperature of the liquid — a rise in temperature increases the kinetic energy of the particles, so more of them cross the surface; clothes dry faster on a hot day.
✗ Humidity of the surrounding air — high humidity means the air already holds a lot of water vapour, so it accepts less; evaporation slows down, which is why clothes dry slowly in the rainy season.
📌 SSC & Railway Exam Facts
• Factors that increase evaporation: greater surface area, higher temperature, lower humidity, higher wind speed.
• Evaporation causes cooling — the particles take latent heat of vaporisation from the surroundings.
• This is why we sweat, why water stays cool in an earthen pot (matka), and why acetone on the palm feels cold.
• Evaporation happens at all temperatures and only at the surface; boiling happens at a fixed temperature and throughout the liquid.
• Latent heat of vaporisation of water = 2260 kJ/kg (22.5 × 10⁵ J/kg).
RRB Technician Grade III 2024-25 – 30 December 2024 Shift 2 · States of matter and their properties

Q40. Which of the following statements is/are correct regarding the liquid state of matter?
Statement I: Liquids have fixed volume but no fixed shape.
Statement II: The rate of diffusion of liquids is higher than that of solids.

  1. (a) Only statement I is correct.
  2. (b) Both statements I and II are correct.
  3. (c) Only statement II is correct.
  4. (d) Neither statement I nor II is correct.
Answer & solution

Answer: (b) Both statements I and II are correct.

Correct Answer: Option 2 — Both statements I and II are correct.
Statement I is correct. In a liquid the particles are held by moderate intermolecular forces — strong enough to keep the particles together, so the volume is fixed, but weak enough to let the particles slide over one another, so a liquid flows and takes the shape of its container. One litre of water stays one litre in a bottle, a beaker or a bowl, but its shape changes each time.
Statement II is also correct. Diffusion is the spontaneous intermixing of particles of two substances. It depends on how freely the particles can move. In a solid the particles only vibrate about fixed positions, so diffusion is extremely slow; in a liquid the particles are free to move about, so diffusion is much faster. The standard order is gas > liquid > solid.
An everyday proof: a drop of ink or copper sulphate spreads through a glass of water in minutes, while two metal blocks pressed together take years to diffuse into each other.
❌ Why the other options are incorrect
✗ Only statement I is correct — statement II is also true; liquid particles move far more freely than solid particles, so they diffuse faster.
✗ Only statement II is correct — statement I is the standard definition of the liquid state and is perfectly true.
✗ Neither statement I nor II is correct — both statements are scientifically correct, so this option is rejected.
📌 SSC & Railway Exam Facts
• Solid — fixed shape and volume; liquid — fixed volume, no fixed shape; gas — neither fixed.
• Rate of diffusion: gas > liquid > solid; compressibility: gas > liquid > solid.
• Intermolecular force: solid > liquid > gas; intermolecular space: gas > liquid > solid.
• Fish survive because oxygen diffuses and dissolves in water — diffusion in a liquid.
• Liquids and gases together are called fluids because both can flow.
RRB Technician Grade III 2024-25 – 30 December 2024 Shift 2 · Interconversion of states (melting, boiling, sublimation, deposition)

Q41. Which of the following is the melting point of ice?

  1. (a) 373.15 K
  2. (b) 273.15 K
  3. (c) 200.15 K
  4. (d) 300.15 K
Answer & solution

Answer: (b) 273.15 K

Correct Answer: Option 2 — 273.15 K
The melting point is the fixed temperature at which a solid changes into a liquid at atmospheric pressure. For ice this temperature is 0 °C.
To convert a Celsius temperature to the Kelvin (SI) scale, add 273.15:
K = °C + 273.15
So the melting point of ice = 0 + 273.15 = 273.15 K (often rounded to 273 K).
While the ice is melting, the temperature does not rise even though heat is being supplied. This heat is used only to break the forces of attraction between the particles and is called the latent heat of fusion. For ice it is 3.34 × 10⁵ J/kg, which is why ice at 0 °C cools a drink far better than water at 0 °C.
❌ Why the other options are incorrect
✗ 373.15 K — this is 100 °C, the boiling point of water, not the melting point of ice; the two values are the classic mix-up in this question.
✗ 200.15 K — this works out to −73 °C, far below the freezing point; ice would remain solid at this temperature.
✗ 300.15 K — this is 27 °C, ordinary room temperature; ice has long since melted by then.
📌 SSC & Railway Exam Facts
• Melting point of ice = 0 °C = 273.15 K; boiling point of water = 100 °C = 373.15 K.
• K = °C + 273.15; °F = (9/5)°C + 32; −40 °C = −40 °F.
• Latent heat of fusion of ice = 3.34 × 10⁵ J/kg; latent heat of vaporisation of water = 22.5 × 10⁵ J/kg.
• Temperature stays constant during a change of state — the heat absorbed is the latent heat.
• Kelvin is the SI unit of temperature; 0 K = −273.15 °C is absolute zero.
RRB Technician Grade III 2024-25 – 29 December 2024 Shift 1 · Interconversion of states (melting, boiling, sublimation, deposition)

Q42. Gas to liquid and liquid to solid conversion is:

  1. (a) condensation and solidification respectively
  2. (b) solidification and condensation respectively
  3. (c) fusion and vaporisation respectively
  4. (d) sublimation and fusion respectively
Answer & solution

Answer: (a) condensation and solidification respectively

Correct Answer: Option 1 — condensation and solidification respectively
Every change of state has its own name, and the direction of the change decides whether heat is absorbed or released.
Gas → liquid is called condensation (also liquefaction). Cooling a gas slows its particles, the intermolecular force of attraction grows strong enough to hold them together, and the gas turns into a liquid. Water droplets forming on a cold glass and the formation of clouds, dew and fog are everyday examples.
Liquid → solid is called solidification (also freezing or fusion in reverse). Cooling removes more energy until the particles can only vibrate about fixed positions. Water freezing into ice at 0 °C (273 K) is the standard example.
Both of these changes are exothermic — the substance gives out its latent heat to the surroundings. The reverse changes, melting and vaporisation, absorb latent heat.
❌ Why the other options are incorrect
✗ solidification and condensation respectively — the two names are in the wrong order; solidification is liquid → solid, not gas → liquid.
✗ fusion and vaporisation respectively — fusion (melting) is solid → liquid and vaporisation is liquid → gas; both are the opposite directions of what is asked.
✗ sublimation and fusion respectively — sublimation is solid → gas directly, without a liquid stage (camphor, naphthalene, dry ice, ammonium chloride, iodine).
📌 SSC & Railway Exam Facts
• Solid → liquid = melting/fusion; liquid → gas = vaporisation; gas → liquid = condensation; liquid → solid = freezing/solidification.
• Solid → gas = sublimation; gas → solid = deposition.
• Melting point of ice = 0 °C = 273 K; boiling point of water = 100 °C = 373 K.
• Latent heat of fusion of ice = 3.34 × 10⁵ J/kg; latent heat of vaporisation of water = 22.5 × 10⁵ J/kg.
• Temperature stays constant during a change of state because the heat supplied is used as latent heat.
RRB Technician Grade III 2024-25 – 29 December 2024 Shift 2 · States of matter and their properties

Q43. Which of the following statements is NOT true regarding the particles of matter?

  1. (a) They are moving constantly.
  2. (b) They do not have spaces in between them.
  3. (c) They are very small.
  4. (d) They attract each other.
Answer & solution

Answer: (b) They do not have spaces in between them.

Correct Answer: Option 2 — They do not have spaces in between them.
The particle nature of matter rests on four established characteristics: particles are extremely small, they have spaces between them, they are continuously moving (they possess kinetic energy), and they attract one another.
The statement in option 2 is the opposite of the truth — particles of matter do have spaces between them. The proof is everyday: when sugar or salt is dissolved in a full glass of water the level does not overflow, because the solute particles slip into the spaces between the water particles. Likewise potassium permanganate spreads through water and two gases mix on their own — both need inter-particle space.
The size of these spaces decides the state: largest in gases, moderate in liquids, smallest in solids — which is why gases are highly compressible and solids are not.
❌ Why the other options are incorrect (they are all TRUE statements)
✗ They are moving constantly — true; particles possess kinetic energy and move ceaselessly, which is shown by diffusion and by Brownian motion. Kinetic energy increases with temperature.
✗ They are very small — true; particles are beyond imagination in smallness — a few crystals of potassium permanganate colour a large bucket of water.
✗ They attract each other — true; this force of attraction holds matter together and is strongest in solids and weakest in gases.
📌 SSC & Railway Exam Facts
• Characteristics of particles: very small, have spaces, always moving, attract each other.
• Inter-particle space and compressibility: gas > liquid > solid; force of attraction: solid > liquid > gas.
• Diffusion increases with temperature, because the kinetic energy of the particles rises.
• Brownian motion — the zig-zag movement of suspended particles — proves that particles are in constant motion.
• Smell of incense spreading, ink diffusing in water and gases mixing are the classic proofs of particle motion and inter-particle space.
RRB Technician Grade III 2024-25 – 29 December 2024 Shift 3 · Evaporation and its factors

Q44. What will happen if you pour some acetone on your palm?

  1. (a) It will cause the palm to feel itchy.
  2. (b) It will cause the palm to feel cool.
  3. (c) It will cause no effect on the palm.
  4. (d) It will cause the palm to feel hot.
Answer & solution

Answer: (b) It will cause the palm to feel cool.

Correct Answer: Option 2 — It will cause the palm to feel cool.
Acetone (propanone, CH₃COCH₃) is a highly volatile liquid — its boiling point is only about 56 °C and the forces holding its molecules together are weak. Poured on the palm, it therefore evaporates very rapidly.
Evaporation is a cooling process. To change from liquid to vapour, the escaping particles must absorb the latent heat of vaporisation, and the nearest source of that heat is the skin of the palm. As heat is drawn out of the palm, its temperature falls and we feel a distinct coolness.
The same physics explains why petrol or spirit spilt on the hand feels cold, why a nurse rubs spirit on the skin before an injection, and why water kept in an earthen pot (matka) stays cool.
❌ Why the other options are incorrect
✗ It will cause the palm to feel itchy — itching is an allergic or irritant response; the ordinary physical effect of acetone on the skin is cooling by evaporation, not itching.
✗ It will cause no effect on the palm — a clear cooling sensation is always felt, because acetone is far more volatile than water.
✗ It will cause the palm to feel hot — the very opposite; evaporation absorbs heat, it never releases it. Heating would require an exothermic change such as condensation.
📌 SSC & Railway Exam Facts
• Evaporation is a surface phenomenon and always causes cooling; it occurs at all temperatures below the boiling point.
• Evaporation is faster with higher temperature, larger surface area, more wind and lower humidity.
• Volatile liquids — acetone, petrol, ether, spirit — evaporate fastest and give the strongest cooling.
• Latent heat of vaporisation of water = 22.5 × 10⁵ J/kg; boiling point of acetone ≈ 56 °C.
• Acetone (propanone) is the simplest ketone, used as a nail-polish remover and a laboratory solvent.
RRB Technician Grade III 2024-25 – 28 December 2024 Shift 1 · Interconversion of states (melting, boiling, sublimation, deposition)

Q45. Which of the following does NOT correctly match a change in the state of matter with its corresponding process?

  1. (a) Liquid to Gas: Evaporation
  2. (b) Gas to Solid: Deposition
  3. (c) Solid to Gas: Sublimation
  4. (d) Gas to Liquid: Sublimation
Answer & solution

Answer: (d) Gas to Liquid: Sublimation

Correct Answer: Option 4 — Gas to Liquid: Sublimation
The change of a gas into a liquid is called condensation (liquefaction), not sublimation. It happens on cooling, when the particles lose kinetic energy and the forces of attraction pull them close enough to form a liquid, and it releases the latent heat of vaporisation. Dew on grass, water droplets on a cold glass and clouds turning into rain are all condensation. This pairing is therefore wrong, which is exactly what the question asks for.
Sublimation is something quite different — the direct change of a solid into a gas without passing through the liquid state. Camphor, naphthalene balls, ammonium chloride, iodine and dry ice (solid CO₂) are the standard sublimating substances.
❌ Why the other options are incorrect
✗ Liquid to Gas: Evaporation — correctly matched; a liquid changing into vapour at any temperature below its boiling point is evaporation (the same change at the boiling point is boiling/vaporisation).
✗ Gas to Solid: Deposition — correctly matched; deposition (desublimation) is the direct change of a gas into a solid, as when frost forms on a cold window.
✗ Solid to Gas: Sublimation — correctly matched; this is the definition of sublimation, shown by camphor and naphthalene.
📌 SSC & Railway Exam Facts
• Solid → Liquid = melting (fusion); Liquid → Solid = freezing (solidification).
• Liquid → Gas = vaporisation/evaporation; Gas → Liquid = condensation.
• Solid → Gas = sublimation; Gas → Solid = deposition.
• Dry ice is solid CO₂; it sublimes directly and is used to keep ice-cream and food cold.
• Melting point of ice = 0 °C (273 K); boiling point of water = 100 °C (373 K) at 1 atm.
RRB Technician Grade III 2024-25 – 28 December 2024 Shift 1 · Interconversion of states (melting, boiling, sublimation, deposition)

Q46. At which of the following temperatures does a liquid change into a solid upon cooling?

  1. (a) Melting point
  2. (b) Freezing point
  3. (c) Boiling point
  4. (d) Condensation point
Answer & solution

Answer: (b) Freezing point

Correct Answer: Option 2 — Freezing point
The freezing point is the fixed temperature at which a liquid changes into a solid on cooling at a given pressure. As the liquid is cooled its particles lose kinetic energy, the intermolecular forces of attraction take over, and the particles settle into the fixed, ordered positions of a solid lattice. The change is called freezing or solidification.
During freezing the temperature does not fall even though heat is still being removed, because the escaping heat is the latent heat of fusion being given out by the particles as they lock into place. For water this value is 3.34 × 10⁵ J/kg.
For a pure substance the freezing point and the melting point are numerically the same — water freezes at 0 °C and ice melts at 0 °C. The two names simply describe the direction of the change: melting is solid → liquid, freezing is liquid → solid.
❌ Why the other options are incorrect
✗ Melting point — the temperature at which a solid turns into a liquid on heating; the value is the same for a pure substance, but the direction of the change is opposite to what the question describes.
✗ Boiling point — the temperature at which a liquid turns into vapour throughout its bulk (water: 100 °C); no solid is formed at all.
✗ Condensation point — the temperature at which a gas turns into a liquid; it is the reverse of boiling, not of melting.
📌 SSC & Railway Exam Facts
• For a pure substance, freezing point = melting point (water/ice = 0 °C = 273 K).
• Latent heat of fusion of ice = 3.34 × 10⁵ J/kg; latent heat of vaporisation of water = 22.5 × 10⁵ J/kg.
• Temperature remains constant during any change of state, as the heat is used as latent heat.
• Water expands on freezing, which is why ice floats and water pipes burst in winter.
• Salt lowers the freezing point of water — the reason salt is spread on icy roads and used in ice-cream making.
RRB Technician Grade III 2024-25 – 28 December 2024 Shift 1 · Evaporation and its factors

Q47. The phenomenon of change of liquid into vapours at any temperature below its boiling point is known as ______.

  1. (a) evaporation
  2. (b) sublimation
  3. (c) fusion
  4. (d) deposition
Answer & solution

Answer: (a) evaporation

Correct Answer: Option 1 — evaporation
Evaporation is the change of a liquid into vapour at any temperature below its boiling point. Unlike boiling, which takes place throughout the liquid at a fixed temperature, evaporation is a surface phenomenon — only the particles at the free surface escape.
The particles of a liquid have different kinetic energies. Some surface particles gain enough kinetic energy to overcome the intermolecular force of attraction and fly off as vapour. Because the fastest particles leave, the average kinetic energy of the liquid left behind falls, and the liquid is cooled — this is why evaporation is a cooling process, absorbing the latent heat of vaporisation from its surroundings.
The rate of evaporation increases with temperature, surface area and wind speed, and decreases with humidity. This is why wet clothes dry faster when spread out on a hot, windy day, and slowly in humid weather.
❌ Why the other options are incorrect
✗ sublimation — the direct change of a solid into a gas without becoming a liquid, shown by camphor, naphthalene, iodine, ammonium chloride and dry ice; no liquid is involved.
✗ fusion — another name for melting, the change of a solid into a liquid on heating (ice → water at 0 °C); it is not a liquid-to-vapour change.
✗ deposition — the direct change of a gas into a solid (frost on a cold window); it is the reverse of sublimation.
📌 SSC & Railway Exam Facts
• Evaporation is a surface phenomenon at all temperatures; boiling occurs throughout the liquid at a fixed temperature.
• Evaporation causes cooling — the reason for sweating, earthen pots (matka) and desert coolers.
• Evaporation ↑ with temperature, surface area, wind speed; ↓ with humidity.
• Latent heat of vaporisation of water = 22.5 × 10⁵ J/kg (2260 kJ/kg).
• Fusion = solid → liquid, Sublimation = solid → gas, Deposition = gas → solid, Condensation = gas → liquid.
RRB Technician Grade III 2024-25 – 28 December 2024 Shift 1 · States of matter and their properties

Q48. Which of the following is NOT a characteristic of a gas?

  1. (a) The particles are very loosely packed.
  2. (b) It is highly compressible.
  3. (c) The rate of diffusion is very high.
  4. (d) It has a fixed shape.
Answer & solution

Answer: (d) It has a fixed shape.

Correct Answer: Option 4 — It has a fixed shape.
A gas has neither a fixed shape nor a fixed volume. Its particles are separated by very large intermolecular spaces and the forces of attraction between them are negligible, so the particles move about randomly at high speed and spread out to completely fill whatever container they are put in. Having a fixed shape is therefore not a property of a gas — it is a property of a solid, so Option 4 is the statement being asked for.
The remaining three statements are all genuine gas properties, and they all follow from the same cause: loose packing and large empty spaces between the particles.
❌ Why the other options are incorrect
✗ The particles are very loosely packed — true; gas particles are the most loosely packed of the three states, which is why a gas has the lowest density.
✗ It is highly compressible — true; the large empty spaces can be squeezed, which is how LPG and CNG are filled into cylinders and oxygen into hospital cylinders.
✗ The rate of diffusion is very high — true; free, fast-moving particles mix quickly, which is why the smell of an agarbatti or perfume spreads across a room within seconds.
📌 SSC & Railway Exam Facts
• Solid → fixed shape and volume; Liquid → fixed volume only; Gas → neither fixed.
• Compressibility and diffusion: gas > liquid > solid; intermolecular force: solid > liquid > gas.
• Gases exert pressure on the walls of the container because of the continuous collisions of their particles.
• LPG = Liquefied Petroleum Gas (mainly butane); CNG = Compressed Natural Gas (mainly methane, CH₄).
• Liquids and gases together are called fluids, as both can flow.
RRB Technician Grade III 2024-25 – 28 December 2024 Shift 2 · States of matter and their properties

Q49. Which of the following is NOT the characteristic of particles of the matter?

  1. (a) They have space between them.
  2. (b) They are very large in size.
  3. (c) They attract each other.
  4. (d) They are continuously moving.
Answer & solution

Answer: (b) They are very large in size.

Correct Answer: Option 2 — They are very large in size.
The particle nature of matter rests on four established characteristics: matter is made of extremely small particles, these particles have space between them, they are continuously moving (they possess kinetic energy), and they attract one another with an intermolecular force of attraction.
Particles of matter are in fact unimaginably small — so small that a few crystals of potassium permanganate can colour a very large volume of water, and the smell of an incense stick spreads across a whole room. Therefore the statement that they are very large in size is NOT a characteristic of matter, and it is the required answer.
The continuous motion of particles causes diffusion, which becomes faster on heating because the kinetic energy of the particles increases.
❌ Why the other options are incorrect
✗ They have space between them — this is true; the intermolecular space is largest in gases and smallest in solids, which is why gases are highly compressible.
✗ They attract each other — this is true; the force of attraction is strongest in solids, moderate in liquids and weakest in gases.
✗ They are continuously moving — this is true; particles possess kinetic energy, which is why diffusion and Brownian motion occur.
📌 SSC & Railway Exam Facts
• Characteristics of particles of matter: very small size, space between them, continuous motion, mutual attraction.
• Intermolecular force: solid > liquid > gas; intermolecular space: gas > liquid > solid.
• Diffusion is fastest in gases and increases with temperature.
• The kinetic energy of particles is directly proportional to the absolute temperature.
• Zig-zag motion of suspended particles is Brownian motion, proof of the continuous motion of particles.
RRB Technician Grade III 2024-25 – 28 December 2024 Shift 3 · Interconversion of states (melting, boiling, sublimation, deposition)

Q50. At what temperature does water transform into steam under normal atmospheric pressure?

  1. (a) 80°C (176°F)
  2. (b) 100°C (212°F)
  3. (c) 50°C (122°F)
  4. (d) 0°C (32°F)
Answer & solution

Answer: (b) 100°C (212°F)

Correct Answer: Option 2 — 100°C (212°F)
The boiling point of a liquid is the temperature at which its vapour pressure becomes equal to the atmospheric pressure, so that the liquid changes rapidly into vapour throughout its bulk, not merely at the surface. For water at normal atmospheric pressure (1 atm = 760 mm of Hg) this temperature is 100 °C, which equals 373 K and 212 °F.
The Fahrenheit value checks out with the standard conversion °F = (°C × 9/5) + 32, giving (100 × 9/5) + 32 = 180 + 32 = 212 °F.
While the water boils, its temperature stays fixed at 100 °C even though heat is still being supplied, because that heat is absorbed as the latent heat of vaporisation (22.5 × 10⁵ J/kg). The boiling point falls as the pressure falls — on a high hill water boils below 100 °C, and cooking there takes longer — while a pressure cooker raises the pressure and so raises the boiling point, cooking food faster.
❌ Why the other options are incorrect
✗ 80°C (176°F) — water only evaporates at this temperature from its surface; it does not boil, as the vapour pressure is still below atmospheric pressure.
✗ 50°C (122°F) — merely warm water; boiling at 50 °C would need the pressure to be lowered to about one-eighth of an atmosphere.
✗ 0°C (32°F) — this is the melting/freezing point of water (273 K), where ice turns into water, not the boiling point.
📌 SSC & Railway Exam Facts
• Boiling point of water = 100 °C = 373 K = 212 °F; melting point of ice = 0 °C = 273 K = 32 °F.
• Conversions: K = °C + 273, °F = (°C × 9/5) + 32; −40 °C = −40 °F.
• Boiling point decreases with decreasing pressure — food is cooked in a pressure cooker at a higher pressure, and so faster, on hills.
• Temperature stays constant during boiling; the heat supplied becomes latent heat of vaporisation = 22.5 × 10⁵ J/kg.
• Boiling is a bulk phenomenon at a fixed temperature; evaporation is a surface phenomenon at all temperatures.
RRB Technician Grade III 2024-25 – 27 December 2024 Shift 1 · States of matter and their properties

Q51. In which of the following matter are particles held together with maximum force?

  1. (a) Perfume
  2. (b) Ink of pen
  3. (c) Water
  4. (d) Iron stick
Answer & solution

Answer: (d) Iron stick

Correct Answer: Option 4 — Iron stick
The force of attraction between particles is greatest in solids, smaller in liquids and least in gases. That single rule decides this question, because only one of the four options is a solid.
An iron stick is a solid. Its particles are very tightly and regularly packed, the interparticle space is minimum and the force of attraction is maximum. This is why a solid has a definite shape and definite volume, is almost incompressible, has a high density and shows a very high rate of rigidity.
• Solid — maximum force of attraction, particles only vibrate about fixed positions.
• Liquid — moderate force, particles slide over one another, definite volume but no definite shape.
• Gas — negligible force, particles move freely at high speed and fill the whole container.
❌ Why the other options are incorrect
✗ Perfume — perfume vapour is a gas, which is precisely why its smell spreads across a room by diffusion; gases have the weakest interparticle force.
✗ Ink of pen — a liquid; its particles move much more freely than those of a solid, so the force between them is far smaller.
✗ Water — also a liquid. It takes the shape of its container and flows, which would be impossible if the attraction were as strong as in a solid.
📌 SSC & Railway Exam Facts
• Force of attraction: solid > liquid > gas; interparticle space and compressibility: gas > liquid > solid.
• Rate of diffusion: gas > liquid > solid; kinetic energy of particles: gas > liquid > solid.
• Solids have definite shape and volume, liquids have definite volume only, gases have neither.
• Gases are highly compressible, which is why LPG and CNG are stored in cylinders and oxygen is carried in hospitals.
• Liquids and gases together are called fluids, because both can flow.
RRB Technician Grade III 2024-25 – 27 December 2024 Shift 2 · States of matter and their properties

Q52. Which of the following states of matter is/are highly compressible?

  1. (a) The liquid state
  2. (b) The solid state
  3. (c) The gaseous state
  4. (d) Both solid state and liquid state
Answer & solution

Answer: (c) The gaseous state

Correct Answer: Option 3 — The gaseous state
Compressibility is the property by which the volume of a substance can be reduced by applying pressure. It depends entirely on the intermolecular space between the particles — the more empty space there is, the more the particles can be pushed together.
In a gas the particles are very far apart, the force of attraction between them is negligible, and they move randomly at high speed. This huge intermolecular space makes gases highly compressible — a large volume of gas can be squeezed into a small cylinder. That is exactly why LPG (liquefied petroleum gas) is supplied in cylinders, CNG (compressed natural gas) runs vehicles, and oxygen is carried in cylinders in hospitals.
In solids the particles are tightly packed with almost no free space, so solids are practically incompressible. In liquids the particles are close but can slide, so liquids are only slightly compressible — far less than gases.
❌ Why the other options are incorrect
✗ The liquid state — liquids are only slightly compressible; their particles are already close together, which is why hydraulic brakes work on the near-incompressibility of liquids.
✗ The solid state — a solid has the smallest intermolecular space and the strongest force of attraction, so it is almost incompressible and rigid.
✗ Both solid state and liquid state — neither is highly compressible; this option confuses fluidity with compressibility.
📌 SSC & Railway Exam Facts
• Compressibility and intermolecular space: gas > liquid > solid; intermolecular force: solid > liquid > gas.
• LPG = Liquefied Petroleum Gas (mainly butane); CNG = Compressed Natural Gas (mainly methane).
• Rate of diffusion: gas > liquid > solid.
• Gases exert pressure on the walls of the container because their particles collide with the walls.
• Liquids and gases together are called fluids because both can flow.
RRB Technician Grade III 2024-25 – 27 December 2024 Shift 2 · Evaporation and its factors

Q53. If the surface area is increased, the rate of evaporation is:

  1. (a) increased
  2. (b) First increases then decreases
  3. (c) constant
  4. (d) decreased
Answer & solution

Answer: (a) increased

Correct Answer: Option 1 — increased
Evaporation is the change of a liquid into vapour at any temperature below its boiling point, and it is a surface phenomenon — only those particles that are at the surface and possess enough kinetic energy can escape into the air.
Because escape happens only from the surface, increasing the surface area exposes more particles to the air, so more particles can escape per second and the rate of evaporation increases. This is why wet clothes spread out on a line dry much faster than the same clothes left in a bundle, and why hot tea is poured into a saucer to cool it quickly.
The rate of evaporation increases with surface area, temperature and wind speed, and decreases with rising humidity, since humid air is already close to saturation with water vapour.
❌ Why the other options are incorrect
✗ First increases then decreases — there is no such reversal; the relationship with surface area is a steady direct (increasing) one.
✗ constant — the rate cannot stay unchanged; more exposed surface always means more escaping particles, a fact demonstrated by drying clothes.
✗ decreased — this is the exact opposite of the truth; reducing the surface area (folding the clothes) is what slows evaporation down.
📌 SSC & Railway Exam Facts
• Evaporation increases with temperature, surface area and wind speed; it decreases with humidity.
• Evaporation is a surface phenomenon and causes cooling; boiling occurs throughout the liquid at a fixed temperature.
• Latent heat of vaporisation of water = 22.5 × 10⁵ J/kg; latent heat of fusion of ice = 3.34 × 10⁵ J/kg.
• Water in an earthen pot (matka) cools because water evaporates through its pores.
• We feel cool under a fan because moving air speeds up the evaporation of sweat.
RRB Technician Grade III 2024-25 – 27 December 2024 Shift 3 · Interconversion of states (melting, boiling, sublimation, deposition)

Q54. A change of state directly from gas to solid without changing into liquid state is called:

  1. (a) vaporisation
  2. (b) solidification
  3. (c) fusion
  4. (d) deposition
Answer & solution

Answer: (d) deposition

Correct Answer: Option 4 — deposition
Deposition (also called desublimation) is the change of a substance directly from the gaseous state to the solid state, with no liquid stage in between. It is the exact reverse of sublimation, in which a solid turns straight into vapour.
It takes place when vapour is cooled so rapidly that its particles lose kinetic energy and are locked into a fixed lattice before they can form a liquid. Deposition is an exothermic change — the vapour must release heat to settle down as a solid.
Familiar examples: the formation of frost on a cold winter morning (water vapour → ice directly), the snowflakes that form in clouds, and the iodine vapour that re-forms shining crystals on the cool upper wall of a vessel after it has sublimed.
❌ Why the other options are incorrect
✗ vaporisation — the change of a liquid into a gas (by boiling or evaporation); it is the wrong direction entirely and involves the liquid state.
✗ solidification — also called freezing, it is the change of a liquid into a solid, e.g. water turning into ice at 0 °C; it starts from a liquid, not a gas.
✗ fusion — another name for melting, the change of a solid into a liquid on absorbing the latent heat of fusion; it is the opposite of freezing.
📌 SSC & Railway Exam Facts
• Sublimation — solid → gas directly; deposition — gas → solid directly.
• Substances that sublime: camphor, naphthalene, iodine, ammonium chloride, dry ice (solid CO₂).
• Melting/fusion — solid → liquid; freezing/solidification — liquid → solid; condensation — gas → liquid.
• Latent heat of fusion of ice = 3.34 × 10⁵ J/kg; latent heat of vaporisation of water = 22.5 × 10⁵ J/kg.
• Frost is a natural example of deposition; dew is a natural example of condensation.
RRB Technician Grade III 2024-25 – 26 December 2024 Shift 1 · Interconversion of states (melting, boiling, sublimation, deposition)

Q55. Which of the following phenomena is used to liquefy gas?

  1. (a) Applying pressure and reducing temperature
  2. (b) Reducing pressure and reducing temperature
  3. (c) Applying pressure and increasing temperature
  4. (d) Applying temperature and reducing pressure
Answer & solution

Answer: (a) Applying pressure and reducing temperature

Correct Answer: Option 1 — Applying pressure and reducing temperature
In a gas the particles are very far apart, move at high speed and have the weakest forces of attraction. To turn a gas into a liquid, these particles must be brought close together and made to move slowly, so that the forces of attraction can hold them.
• Applying high pressure squeezes the particles into a much smaller volume, greatly reducing the space between them.
• Lowering the temperature reduces the kinetic energy of the particles, so they can no longer overcome the attractive forces.
Applying both together is exactly how gases are liquefied industrially — LPG in cylinders, CNG, and liquid oxygen, nitrogen and ammonia. Above a certain temperature, called the critical temperature, a gas cannot be liquefied by pressure alone, which is why cooling is essential.
❌ Why the other options are incorrect
✗ Reducing pressure and reducing temperature — reducing pressure lets the gas expand and its particles move further apart, which works against liquefaction.
✗ Applying pressure and increasing temperature — raising the temperature gives particles more kinetic energy to escape, exactly the opposite of what liquefaction needs.
✗ Applying temperature and reducing pressure — both changes push the substance towards the gaseous state; this is how a liquid is made to vaporise, not condense.
📌 SSC & Railway Exam Facts
• Interparticle force: solid > liquid > gas; interparticle distance: gas > liquid > solid.
• Compressibility: gases are highly compressible, liquids very slightly, solids almost none.
• LPG = Liquefied Petroleum Gas (mainly butane + propane); CNG = Compressed Natural Gas (mainly methane).
• Dry ice is solid CO₂ kept under high pressure; on release it sublimes.
• Above the critical temperature no amount of pressure can liquefy a gas.
RRB Technician Grade III 2024-25 – 26 December 2024 Shift 1 · Diffusion

Q56. What happens to the process of diffusion on heating?

  1. (a) There is no effect of heating on diffusion.
  2. (b) On heating, diffusion becomes faster.
  3. (c) On heating, diffusion becomes slower.
  4. (d) Diffusion depends on volume of matter.
Answer & solution

Answer: (b) On heating, diffusion becomes faster.

Correct Answer: Option 2 — On heating, diffusion becomes faster.
Diffusion is the spontaneous intermixing of the particles of two substances on their own, because the particles of matter are continuously moving and possess kinetic energy.
On heating, the particles absorb heat energy, so their kinetic energy and speed increase. Faster-moving particles spread into the other substance more quickly, and therefore the rate of diffusion increases with a rise in temperature.
Everyday proof: a crystal of potassium permanganate colours hot water far faster than cold water; incense or perfume spreads much more quickly in a warm room; tea leaves release colour faster in hot water than in cold.
The rate of diffusion is fastest in gases, slower in liquids and negligible in solids, because the interparticle space and freedom of movement decrease in that order.
❌ Why the other options are incorrect
✗ There is no effect of heating on diffusion. — wrong; temperature is the main factor controlling the rate of diffusion.
✗ On heating, diffusion becomes slower. — the opposite is true; heat increases particle speed, so diffusion speeds up.
✗ Diffusion depends on volume of matter. — diffusion depends mainly on temperature, state of matter and particle size (mass), not on volume.
📌 SSC & Railway Exam Facts
• Rate of diffusion: gases > liquids > solids.
• Rate of diffusion increases with temperature and decreases with larger particle mass.
• Diffusion proves that matter is made of tiny particles that are constantly moving.
• Smelling food or perfume from a distance, and the spread of ink in water, are classic examples.
• Diffusion in solids is extremely slow but real — e.g. two metal blocks pressed together for years.
RRB Technician Grade III 2024-25 – 26 December 2024 Shift 1 · States of matter and their properties

Q57. Which of the following pairs is an example of a solid state of matter?

  1. (a) Juice and milk
  2. (b) Oil and sugar
  3. (c) Sugar and sponge
  4. (d) Water and oxygen
Answer & solution

Answer: (c) Sugar and sponge

Correct Answer: Option 3 — Sugar and sponge
A solid has a definite shape, distinct boundaries and a fixed volume. Its particles are very closely packed, the force of attraction between them is the strongest, and they can only vibrate about fixed positions. Solids are almost incompressible and rigid.
Both members of this pair are solids:
• Sugar is a crystalline solid with a definite shape and fixed volume.
• A sponge is a solid too. It can be compressed only because it is full of tiny air-filled pores — the sponge material itself does not shrink, the trapped air is squeezed out. So a sponge is the classic exam example of a compressible solid.
❌ Why the other options are incorrect
✗ Juice and milk — both are liquids; they take the shape of the container and have a fixed volume but no fixed shape.
✗ Oil and sugar — oil is a liquid, so the pair is mixed; only sugar is solid.
✗ Water and oxygen — water is a liquid and oxygen is a gas; a gas has neither a fixed shape nor a fixed volume.
📌 SSC & Railway Exam Facts
• Solid — definite shape and volume; liquid — definite volume, no definite shape; gas — neither.
• Interparticle force: solid > liquid > gas; compressibility: gas > liquid > solid.
• Rate of diffusion: gas > liquid > solid.
• Sponge is the standard example of a solid that can be compressed (because of trapped air).
• Rubber band shows that a solid can change shape under force yet remain a solid.
RRB Technician Grade III 2024-25 – 26 December 2024 Shift 2 · States of matter and their properties

Q58. As the temperature increases, the kinetic energy of particles of matter _______.

  1. (a) increases
  2. (b) decreases
  3. (c) remains the same
  4. (d) becomes zero
Answer & solution

Answer: (a) increases

Correct Answer: Option 1 — increases
According to the kinetic theory of matter, all matter is made of tiny particles that are in continuous random motion and therefore always possess kinetic energy.
Temperature is a direct measure of the average kinetic energy of these particles. When a substance is heated, the supplied heat energy is converted into the kinetic energy of its particles, so the particles vibrate and move faster, the spaces between them grow, and the force of attraction between them weakens. This is exactly why heating makes solids melt and liquids boil, and why the rate of diffusion and evaporation both rise with temperature.
Mathematically, the average kinetic energy of a particle is directly proportional to the absolute temperature in kelvin, and it becomes zero only at absolute zero, 0 K = −273 °C.
❌ Why the other options are incorrect
✗ decreases — kinetic energy falls only on cooling; that is how a gas is liquefied by lowering the temperature.
✗ remains the same — the kinetic energy stays constant only if the temperature is constant, as during a change of state when the heat supplied acts as latent heat.
✗ becomes zero — particle motion would stop completely only at absolute zero (0 K = −273 °C), a temperature that can never actually be reached.
📌 SSC & Railway Exam Facts
• K = °C + 273; 0 °C = 273 K and 100 °C = 373 K.
• Order of kinetic energy of particles: gas > liquid > solid.
• Latent heat is absorbed during a change of state without any rise in temperature.
• Latent heat of fusion of ice = 3.34 × 10⁵ J/kg; latent heat of vaporisation of water = 22.5 × 10⁵ J/kg.
• Evaporation is a surface phenomenon and it causes cooling, which is why a desert cooler works.
RRB Technician Grade III 2024-25 – 26 December 2024 Shift 2 · Physical and chemical changes

Q59. Which of the following observable changes indicate that a chemical reaction has occurred?
(a) Formation of gas
(b) Formation of precipitates
(c) Change in physical state
(d) Colour change

  1. (a) Only (a) and (b)
  2. (b) Only (a), (b) and (c)
  3. (c) Only (c) and (d)
  4. (d) All (a), (b), (c) and (d)
Answer & solution

Answer: (d) All (a), (b), (c) and (d)

Correct Answer: Option 4 — All (a), (b), (c) and (d)
A chemical reaction takes place when the reactants are converted into new substances with new properties. NCERT lists the observations that tell us a chemical reaction has taken place as: change in state, change in colour, evolution of a gas, and change in temperature, to which the formation of a precipitate is added.
All four statements in the question are among these recognised indicators, so all of them are correct.
⚗️ One example of each
• Gas evolved — Zn + H₂SO₄ → ZnSO₄ + H₂↑, brisk effervescence of hydrogen.
• Precipitate formed — Pb(NO₃)₂ + 2KI → PbI₂(s) + 2KNO₃, the yellow precipitate of lead iodide.
• Change in state — burning of a candle turns solid wax into CO₂ and water vapour.
• Colour change — Fe + CuSO₄ → FeSO₄ + Cu, in which the blue solution turns pale green.
❌ Why the other options are incorrect
✗ Only (a) and (b) — it wrongly leaves out change of state and colour change, both of which are standard textbook indicators.
✗ Only (a), (b) and (c) — colour change is omitted, yet it is the very observation used in the iron–copper sulphate experiment.
✗ Only (c) and (d) — this omits the evolution of a gas and the formation of a precipitate, the two most obvious signs of a reaction in the laboratory.
📌 SSC & Railway Exam Facts
• Signs of a chemical change: change in state, colour, temperature, evolution of gas, formation of a precipitate.
• A chemical change is usually irreversible; a physical change is generally reversible.
• Rusting of iron and souring of milk are chemical changes; melting of ice is a physical change.
• Reactions that release heat are exothermic; those that absorb heat are endothermic.
• Respiration is an exothermic reaction; photosynthesis is endothermic.
RRB Technician Grade III 2024-25 – 26 December 2024 Shift 2 · Diffusion

Q60. The rate of diffusion of liquids is higher than that of solids because:

  1. (a) in the liquid state, particles do not move freely, but have greater space between each other
  2. (b) in the liquid state, particles do not move freely and do not have greater space between each other
  3. (c) in the liquid state, particles move freely and have greater space between each other
  4. (d) in the liquid state, particles only move freely and do not have greater space between each other
Answer & solution

Answer: (c) in the liquid state, particles move freely and have greater space between each other

Correct Answer: Option 3 — in the liquid state, particles move freely and have greater space between each other
Diffusion is the spontaneous intermixing of the particles of two substances on their own. Its rate depends on two things — how freely the particles can move and how much empty space is available between them.
In a solid the particles are very tightly packed, the interparticle space is minimum and the force of attraction is maximum, so the particles can only vibrate about a fixed position. Diffusion in solids is therefore extremely slow.
In a liquid the particles are less tightly packed, the interparticle space is larger and the force of attraction is weaker, so the particles can slide and move freely over one another. Both required conditions are satisfied, which is why liquids diffuse much faster than solids.
Dropping ink or copper sulphate crystals into a beaker of water and watching the colour spread is the standard demonstration.
❌ Why the other options are incorrect
✗ particles do not move freely, but have greater space — only half true; liquid particles do move freely, which is exactly why a liquid flows and takes the shape of its container.
✗ particles do not move freely and do not have greater space — this describes a solid, not a liquid.
✗ particles only move freely and do not have greater space — the increased interparticle space in a liquid is real and is essential for faster diffusion.
📌 SSC & Railway Exam Facts
• Rate of diffusion: gases > liquids > solids.
• Diffusion increases with a rise in temperature because particle kinetic energy increases.
• Order of interparticle space and compressibility: gas > liquid > solid; order of density and force of attraction: solid > liquid > gas.
• Solids do diffuse, but very slowly — the classic example is solid ammonium chloride sublimating, or gold foil diffusing into lead over years.
• Liquids and gases are together called fluids because both can flow.
RRB Technician Grade III 2024-25 – 26 December 2024 Shift 2 · Interconversion of states (melting, boiling, sublimation, deposition)

Q61. Which of the following is NOT a phase transition between the states of matter?

  1. (a) Vaporization
  2. (b) Sublimation
  3. (c) Condensation
  4. (d) Emission
Answer & solution

Answer: (d) Emission

Correct Answer: Option 4 — Emission
A phase transition (change of state) is the conversion of matter from one physical state into another — solid, liquid or gas — brought about by a change of temperature or pressure, while the chemical composition stays exactly the same. It is therefore a physical change and is reversible.
Emission simply means the giving out of energy, light, radiation or particles by a body — for example the emission of light by a bulb or of radiation by a radioactive nucleus. No solid, liquid or gas is converted into another state, so emission is not a phase transition, and it is the required answer.
❌ Why the other options are incorrect (i.e. they ARE phase transitions)
✗ Vaporization — the change from liquid to gas on absorbing heat, as when water boils at 100 °C to give steam.
✗ Sublimation — the direct change from solid to gas without passing through the liquid state, shown by camphor, naphthalene, iodine, ammonium chloride and dry ice.
✗ Condensation — the change from gas to liquid on cooling, seen as dew on a cold glass and in the formation of clouds.
📌 SSC & Railway Exam Facts
• The six phase transitions: melting (fusion), freezing (solidification), vaporisation, condensation, sublimation, deposition.
• Deposition is the reverse of sublimation — gas directly to solid, as in the formation of frost.
• Melting point of ice = 0 °C = 273 K; boiling point of water = 100 °C = 373 K at 1 atm.
• Evaporation occurs at all temperatures and only at the surface; boiling occurs at a fixed temperature throughout the liquid.
• During a change of state the temperature does not rise — the heat taken in is the latent heat.
RRB Technician Grade III 2024-25 – 26 December 2024 Shift 3 · Evaporation and its factors

Q62. In which state of matter does evaporation occur?

  1. (a) Liquid only
  2. (b) Both plasma and liquid
  3. (c) Solid only
  4. (d) Plasma only
Answer & solution

Answer: (a) Liquid only

Correct Answer: Option 1 — Liquid only
Evaporation is the change of a liquid into its vapour at any temperature below its boiling point. It is purely a surface phenomenon — only those particles lying at the surface of the liquid that happen to gain enough kinetic energy can overcome the force of attraction of their neighbours and escape into the air.
Since the process needs a free liquid surface from which particles can fly off, evaporation takes place only in the liquid state.
Evaporation is faster when the surface area is larger, the temperature is higher, the humidity is lower, and the wind speed is greater. The escaping particles carry away energy, so evaporation always causes cooling — that is why we sweat, why water stays cool in an earthen pot, and why a desert cooler works.
❌ Why the other options are incorrect
✗ Both plasma and liquid — plasma is the ionised, super-energetic fourth state of matter found in the Sun, stars and fluorescent tubes; its particles are already free ions and electrons, so evaporation does not apply to it.
✗ Solid only — a solid changing directly into vapour is called sublimation, not evaporation, as in camphor, naphthalene, iodine and dry ice.
✗ Plasma only — evaporation is entirely a property of liquids; plasma is created by supplying very high energy to a gas, an altogether different process.
📌 SSC & Railway Exam Facts
• Evaporation — at all temperatures, only at the surface, a slow and cooling process.
• Boiling — at a fixed temperature, throughout the bulk of the liquid, a rapid process.
• The five states of matter: solid, liquid, gas, plasma and Bose–Einstein condensate (BEC).
• Plasma is the most abundant state of matter in the universe; BEC was obtained by cooling to near 0 K.
• Latent heat of vaporisation of water = 22.5 × 10⁵ J/kg, which is why steam burns are worse than boiling-water burns.
RRB Technician Grade III 2024-25 – 24 December 2024 Shift 1 · Evaporation and its factors

Q63. Which of the following phenomena is the reason behind wearing cotton clothes in summer?

  1. (a) Sublimation
  2. (b) Condensation
  3. (c) Fusion
  4. (d) Evaporation
Answer & solution

Answer: (d) Evaporation

Correct Answer: Option 4 — Evaporation
Evaporation is the change of a liquid into vapour at any temperature and only from the surface of the liquid. The particles that escape are the ones with the highest kinetic energy; to leave, they absorb the latent heat of vaporisation from their surroundings, so the surface left behind becomes cooler. This is why evaporation causes cooling.
In summer the body throws out sweat. Cotton is a good absorber of water and is highly porous, so it soaks up the sweat and exposes it to the air over a large area. The sweat then evaporates rapidly, taking heat from the body and leaving us feeling cool and comfortable. Synthetic fabrics neither absorb nor release sweat easily, so they feel sticky and hot.
❌ Why the other options are incorrect
✗ Sublimation — the change of a solid directly into a gas, as with camphor, naphthalene and dry ice; no solid is involved in sweating.
✗ Condensation — the change of a gas into a liquid, as when dew or fog forms; it releases heat instead of absorbing it.
✗ Fusion — the change of a solid into a liquid (melting), such as ice → water; again irrelevant to cooling by sweat.
📌 SSC & Railway Exam Facts
• Evaporation happens at all temperatures, only at the surface; boiling happens at a fixed boiling point throughout the liquid.
• Rate of evaporation increases with temperature, surface area and wind speed, and decreases with humidity.
• Latent heat of vaporisation of water = 22.5 × 10⁵ J/kg; latent heat of fusion of ice = 3.34 × 10⁵ J/kg.
• Water in an earthen pot stays cool because water evaporates from its pores.
• Solid → gas = sublimation; gas → solid = deposition; liquid → gas = vaporisation; gas → liquid = condensation.
RRB Technician Grade III 2024-25 – 24 December 2024 Shift 1 · Interconversion of states (melting, boiling, sublimation, deposition)

Q64. Which of the following statements is/are correct regarding the effects of changes in pressure on the states of matter?
Statement I: Applying pressure and reducing temperature can liquefy gases.
Statement II: Solid carbon dioxide is stored under high pressure.

  1. (a) Only statement I is correct.
  2. (b) Both statements I and II are correct.
  3. (c) Neither statement I nor II is correct.
  4. (d) Only statement II is correct.
Answer & solution

Answer: (b) Both statements I and II are correct.

Correct Answer: Option 2 — Both statements I and II are correct
The state of a substance depends on both temperature and pressure. Increasing the pressure pushes the particles closer together; lowering the temperature reduces their kinetic energy. Both changes strengthen the force of attraction between particles.
Statement I is correct — a gas is converted into a liquid by applying high pressure and lowering the temperature. This is exactly how LPG is filled into cylinders and how oxygen and nitrogen are supplied as liquids. Each gas has a critical temperature above which no amount of pressure can liquefy it.
Statement II is correct — solid carbon dioxide (dry ice) is stored under high pressure. When the pressure is reduced to 1 atmosphere, it changes directly into CO₂ gas by sublimation, leaving no liquid behind.
❌ Why the other options are incorrect
✗ Only statement I is correct — it wrongly rejects II; dry ice really is kept under high pressure.
✗ Neither statement I nor II is correct — both are standard NCERT statements about the effect of pressure.
✗ Only statement II is correct — it wrongly rejects I; liquefaction of gases by pressure + cooling is a basic fact.
📌 SSC & Railway Exam Facts
• Gas → liquid by increasing pressure and decreasing temperature.
• Solid CO₂ = dry ice; it sublimes at about −78 °C, used as a refrigerant.
• LPG cylinders contain liquefied butane and propane under pressure.
• Interparticle force: solid > liquid > gas; compressibility: gas > liquid > solid.
• Plasma is the fourth state and BEC the fifth state of matter.
RRB Technician Grade III 2024-25 – 24 December 2024 Shift 1 · Interconversion of states (melting, boiling, sublimation, deposition)

Q65. A gas can be liquefied by ______.

  1. (a) low pressure and high temperature
  2. (b) high pressure and high temperature
  3. (c) low pressure and low temperature
  4. (d) high pressure and low temperature
Answer & solution

Answer: (d) high pressure and low temperature

Correct Answer: Option 4 — high pressure and low temperature
In a gas the particles are very far apart, move at high speed and the force of attraction between them is negligible. To convert a gas into a liquid, the particles must be brought closer together and their kinetic energy must be reduced.
• Increasing the pressure squeezes the particles into a smaller volume, so the interparticle distance decreases and the force of attraction becomes effective.
• Decreasing the temperature lowers the kinetic energy of the particles, so they can no longer overcome that attraction and stay bound together.
When both are done together, the gas liquefies. This is exactly how LPG is filled into cylinders and how liquid oxygen and liquid nitrogen are produced. Above a gas's critical temperature no amount of pressure can liquefy it, so cooling is essential.
❌ Why the other options are incorrect
✗ low pressure and high temperature — both changes push the particles further apart and raise their energy; this favours evaporation, the exact opposite of liquefaction.
✗ high pressure and high temperature — high pressure helps, but high temperature gives the particles enough energy to escape again.
✗ low pressure and low temperature — low temperature helps, but low pressure lets the particles spread out; reducing pressure even makes a liquid boil more easily.
📌 SSC & Railway Exam Facts
• Gas → liquid = increase pressure + decrease temperature.
• LPG = butane + propane, stored liquefied under pressure; CNG is stored compressed, not liquefied.
• Liquid nitrogen boils at −196 °C and is used to preserve semen, blood and vaccines.
• Kelvin scale: K = °C + 273; 0 K = −273.15 °C is absolute zero.
• Each gas has a critical temperature above which it cannot be liquefied by pressure alone.
RRB Technician Grade III 2024-25 – 24 December 2024 Shift 1 · Physical and chemical changes

Q66. Formation of the mixture is a _______ change whereas formation of a compound is a _______ change, respectively.

  1. (a) chemical, physical
  2. (b) physical, physical
  3. (c) physical, chemical
  4. (d) chemical, chemical
Answer & solution

Answer: (c) physical, chemical

Correct Answer: Option 3 — physical, chemical
A physical change alters only the appearance, state or form of a substance; no new substance is produced and the change is usually reversible. A chemical change produces a completely new substance with new properties and is generally irreversible, often accompanied by a change of energy.
When a mixture is made, the substances are only mixed in any proportion; each keeps its own properties and can be recovered by physical methods such as filtration, magnetic separation or distillation. Hence forming a mixture is a physical change.
When a compound is formed, the elements combine chemically in a fixed ratio by mass. A completely new substance appears, heat or light is absorbed or released, and it can be separated only by chemical means. Hence forming a compound is a chemical change.
• Iron filings + sulphur powder mixed → a mixture; iron is still attracted by a magnet.
• Iron filings + sulphur heated → iron sulphide (FeS), a compound; the magnet no longer attracts it.
❌ Why the other options are incorrect
✗ chemical, physical — this is the exact reverse; forming a mixture involves no new substance at all.
✗ physical, physical — forming a compound gives a new substance, so it cannot be physical.
✗ chemical, chemical — mixing needs no chemical reaction, so the first blank cannot be chemical.
📌 SSC & Railway Exam Facts
• Mixture: variable composition, physical change, separable by physical methods.
• Compound: fixed composition, chemical change, separable by chemical methods only.
• Physical change: melting of ice, boiling of water, dissolving sugar, glowing of a bulb filament.
• Chemical change: rusting of iron, burning of paper, curdling of milk, cooking of food.
• Law of Constant Proportions (Proust): a compound always has the same elements in the same ratio by mass.
RRB Technician Grade III 2024-25 – 24 December 2024 Shift 2 · Interconversion of states (melting, boiling, sublimation, deposition)

Q67. The temperature at which a liquid starts boiling at atmospheric pressure is known as ______.

  1. (a) triple point
  2. (b) fusion point
  3. (c) boiling point
  4. (d) melting point
Answer & solution

Answer: (c) boiling point

Correct Answer: Option 3 — boiling point
The boiling point of a liquid is the temperature at which its vapour pressure becomes equal to the atmospheric pressure, so that bubbles of vapour form throughout the bulk of the liquid and it changes rapidly into vapour. At 1 atmosphere (101.3 kPa) pure water boils at 100 °C (373 K).
While a liquid boils its temperature does not rise, even though heat is being supplied. This heat is used up as the latent heat of vaporisation — for water 22.5 × 10⁵ J/kg — to overcome the forces of attraction between the molecules.
The boiling point increases with pressure, which is why a pressure cooker cooks food faster, and decreases at high altitudes, which is why water boils below 100 °C on a hill.
❌ Why the other options are incorrect
✗ triple point — the single temperature and pressure at which solid, liquid and gas coexist in equilibrium (for water, 0.01 °C); it is not the boiling temperature.
✗ fusion point — another name for the melting point, the solid → liquid change, not the liquid → gas change.
✗ melting point — the temperature at which a solid turns into a liquid (ice melts at 0 °C / 273 K).
📌 SSC & Railway Exam Facts
• Boiling point of water = 100 °C = 373 K; melting point of ice = 0 °C = 273 K.
• K = °C + 273.
• Boiling is a bulk phenomenon at a fixed temperature; evaporation is a surface phenomenon at all temperatures.
• Latent heat of vaporisation of water = 22.5 × 10⁵ J/kg; latent heat of fusion of ice = 3.34 × 10⁵ J/kg.
• Adding a non-volatile solute (salt) raises the boiling point and lowers the freezing point.
RRB Technician Grade III 2024-25 – 24 December 2024 Shift 2 · Evaporation and its factors

Q68. Which of the following factors decreases the rate of evaporation?

  1. (a) Increase in surface area
  2. (b) Increase in humidity
  3. (c) Increase in wind speed
  4. (d) Increase in temperature
Answer & solution

Answer: (b) Increase in humidity

Correct Answer: Option 2 — Increase in humidity
Evaporation is the change of a liquid into vapour from its surface at any temperature, even below the boiling point. Its rate increases with surface area, temperature and wind speed, but it decreases when humidity increases.
Humidity is the amount of water vapour already present in the air. When humidity is high, the air is nearly saturated and can hold very little extra vapour, so molecules that escape from the liquid surface are pushed back into it. The net rate of evaporation therefore falls. This is exactly why clothes take a very long time to dry on a humid, rainy day and dry quickly in dry summer air.
Evaporation always causes cooling, because the fastest (most energetic) molecules leave the liquid and carry away latent heat.
❌ Why the other options are incorrect
✗ Increase in surface area — a bigger exposed surface lets more molecules escape, so evaporation increases; hot tea cools faster in a saucer than in a cup.
✗ Increase in wind speed — moving air sweeps the vapour away and keeps the air above the liquid unsaturated, so evaporation increases.
✗ Increase in temperature — more molecules gain enough kinetic energy to escape the surface, so evaporation increases.
📌 SSC & Railway Exam Facts
• Rate of evaporation ∝ surface area, temperature, wind speed; ∝ 1/humidity.
• Water stays cool in an earthen pot (matka) because it evaporates through the pores.
• Sweating cools the body by evaporation.
• Evaporation — surface phenomenon at all temperatures; boiling — bulk phenomenon at a fixed temperature.
• Evaporation is a cooling process; it absorbs latent heat of vaporisation.
RRB Technician Grade III 2024-25 – 24 December 2024 Shift 2 · Interconversion of states (melting, boiling, sublimation, deposition)

Q69. In which of the following phenomena is solid state directly transformed into gaseous state without changing into liquid state?

  1. (a) Fusion
  2. (b) Deposition
  3. (c) Sublimation
  4. (d) Solidification
Answer & solution

Answer: (c) Sublimation

Correct Answer: Option 3 — Sublimation
Sublimation is the change of a substance directly from the solid state to the gaseous state without passing through the liquid state. It occurs in solids whose particles are held by weak intermolecular forces and which have a high vapour pressure even at ordinary temperature. The process absorbs the latent heat of sublimation.
The common subliming solids are camphor, naphthalene (mothballs), ammonium chloride (NH₄Cl), iodine, anthracene and dry ice (solid CO₂).
This property is used as a separation technique: a mixture of camphor and common salt, or NH₄Cl and sand, is heated in a china dish covered with an inverted funnel — the subliming solid vaporises and re-solidifies on the cool funnel.
❌ Why the other options are incorrect
✗ Fusion — this is melting, the change of a solid into a liquid at its melting point.
✗ Deposition — the reverse of sublimation: a gas changes directly into a solid (formation of frost or snow), not solid → gas.
✗ Solidification — this is freezing, the change of a liquid into a solid.
📌 SSC & Railway Exam Facts
• Solid → gas = sublimation; gas → solid = deposition.
• Liquid → gas = vaporisation; gas → liquid = condensation; solid → liquid = fusion/melting.
• Dry ice is solid CO₂; it sublimes at −78.5 °C and is used as a refrigerant.
• Classic subliming solids: camphor, naphthalene, NH₄Cl, iodine, anthracene.
• Sublimation is used to purify camphor, naphthalene and iodine in the laboratory.
RRB Technician Grade III 2024-25 – 24 December 2024 Shift 3 · Interconversion of states (melting, boiling, sublimation, deposition)

Q70. During the deposition procedure, which type of state conversion will take place?

  1. (a) Solid to liquid state
  2. (b) Solid to gaseous state
  3. (c) Liquid to solid state
  4. (d) Gaseous to solid state
Answer & solution

Answer: (d) Gaseous to solid state

Correct Answer: Option 4 — Gaseous to solid state
Deposition (also called desublimation) is the change of a substance directly from the gaseous state to the solid state, without passing through the liquid state. It is the exact reverse of sublimation, and it releases the latent heat that sublimation absorbs.
Everyday examples: the formation of frost on a cold winter morning, the formation of snow high in the atmosphere, and the white solid ring of ammonium chloride that forms on the cool walls of a tube when NH₃ and HCl vapours meet. In the laboratory, iodine vapour deposits as shining violet crystals on the cold inner surface of an inverted funnel.
❌ Why the other options are incorrect
✗ Solid to liquid state — this is melting (fusion), which takes place at the melting point, e.g. ice at 0 °C.
✗ Solid to gaseous state — this is sublimation, the opposite process; camphor, naphthalene and NH₄Cl sublime.
✗ Liquid to solid state — this is freezing (solidification), e.g. water turning into ice.
📌 SSC & Railway Exam Facts
• Gas → solid = deposition; solid → gas = sublimation.
• Liquid → gas = vaporisation; gas → liquid = condensation; liquid → solid = freezing.
• Deposition is an exothermic change — it releases the latent heat of sublimation.
• Frost and snow are the standard natural examples of deposition.
• Interparticle force: solid > liquid > gas; interparticle space: gas > liquid > solid.
RRB Technician Grade III 2024-25 – 23 December 2024 Shift 1 · States of matter and their properties

Q71. Which of the following options does NOT represent a characteristic of solids?

  1. (a) Solids have indistinct boundaries.
  2. (b) Solids have a definite shape.
  3. (c) Solids have negligible compressibility.
  4. (d) Solids have fixed volume.
Answer & solution

Answer: (a) Solids have indistinct boundaries.

Correct Answer: Option 1 — Solids have indistinct boundaries.
The question asks which statement is NOT true of solids. In a solid the particles are packed very close together, the intermolecular force of attraction is the strongest and the intermolecular space is the least, so the particles can only vibrate about fixed positions and cannot move from place to place.
This rigid arrangement gives solids their standard properties: a definite shape, a fixed volume, distinct (sharp) boundaries, negligible compressibility, a high density and rigidity. A solid therefore always has a distinct boundary, and the statement "Solids have indistinct boundaries" is false — which is exactly what the question is asking for.
It is gases that have no distinct boundary at all: a gas spreads out and completely fills whatever container it is placed in.
❌ Why the other options are incorrect (they ARE true of solids)
✗ Solids have a definite shape — true; the strong intermolecular forces lock the particles in fixed positions, so the shape does not change with the container.
✗ Solids have negligible compressibility — true; the intermolecular space is already at a minimum, so a solid can hardly be squeezed any further.
✗ Solids have fixed volume — true; a solid keeps both its shape and its volume unless it is heated or a large force is applied.
📌 SSC & Railway Exam Facts
• Solids: definite shape, definite volume, distinct boundary, high density, rigid, negligible compressibility.
• Liquids have a definite volume but no definite shape; gases have neither shape nor volume fixed.
• Intermolecular force: solid > liquid > gas; intermolecular space: gas > liquid > solid.
• A rubber band changes shape and a sponge can be compressed, yet both are still solids.
• Sublimation — a solid changing directly into vapour: camphor, naphthalene, iodine, ammonium chloride and dry ice.
RRB Technician Grade III 2024-25 – 23 December 2024 Shift 1 · States of matter and their properties

Q72. Which statement is true for solid matter?

  1. (a) Solids do not have a definite shape, distinct boundary and fixed volume.
  2. (b) Solids have a definite shape, distinct boundary and fixed volume.
  3. (c) Solids have only definite shape, but not fixed volume.
  4. (d) Solids have only definite shape, but not distinct boundary.
Answer & solution

Answer: (b) Solids have a definite shape, distinct boundary and fixed volume.

Correct Answer: Option 2 — Solids have a definite shape, distinct boundary and fixed volume.
In a solid the particles are packed extremely close together. The intermolecular force of attraction is maximum and the intermolecular space is minimum, so each particle can only vibrate about its own fixed position and cannot travel from place to place.
Because of this rigid arrangement a solid has:
• a definite shape, which does not change with the container,
• a fixed volume,
• a distinct (sharp) boundary,
• negligible compressibility and a high density,
• rigidity — a large force is needed to change its shape.
All three properties listed in Option 2 — definite shape, distinct boundary and fixed volume — therefore belong together to the solid state, and that makes it the only true statement here.
❌ Why the other options are incorrect
✗ Solids do not have a definite shape, distinct boundary and fixed volume — this actually describes a gas, which fills its container completely and has no boundary of its own.
✗ Solids have only definite shape, but not fixed volume — a solid's volume is fixed as well; a substance with a fixed volume but no fixed shape is a liquid.
✗ Solids have only definite shape, but not distinct boundary — a sharp boundary is the most obvious feature of a solid; only gases lack a distinct boundary.
📌 SSC & Railway Exam Facts
• Solid — fixed shape + fixed volume; liquid — fixed volume only; gas — neither fixed.
• Density: solid > liquid > gas; compressibility: gas > liquid > solid.
• Diffusion is fastest in gases and slowest (almost nil) in solids.
• Solid → liquid = melting (fusion); liquid → gas = vaporisation; solid → gas = sublimation.
• Latent heat of fusion of ice = 3.34 × 10⁵ J/kg; latent heat of vaporisation of water = 22.5 × 10⁵ J/kg.
RRB Technician Grade III 2024-25 – 23 December 2024 Shift 2 · Diffusion

Q73. Which of the following is a property of liquids?

  1. (a) Liquids are rigid.
  2. (b) The rate of diffusion of liquids is higher than that of solids.
  3. (c) Liquids have fixed shape.
  4. (d) Liquids have no fixed volume.
Answer & solution

Answer: (b) The rate of diffusion of liquids is higher than that of solids.

Correct Answer: Option 2 — The rate of diffusion of liquids is higher than that of solids
Diffusion is the spontaneous intermixing of the particles of two substances on their own. Its rate depends on how freely the particles can move, which in turn depends on the intermolecular force and the space between particles.
In a solid the particles only vibrate about fixed positions — the intermolecular force is strongest and the particles are most closely packed, so diffusion is extremely slow. In a liquid the particles are still close together but can slide over one another, so diffusion is clearly faster than in solids (though slower than in gases). Copper sulphate crystals dissolving and colouring still water, or ink spreading in water, are the standard examples.
The order of the rate of diffusion is therefore gases > liquids > solids.
❌ Why the other options are incorrect
✗ Liquids are rigid — rigidity belongs to solids; liquids show fluidity and flow.
✗ Liquids have fixed shape — a liquid takes the shape of its container; only solids have a definite shape.
✗ Liquids have no fixed volume — liquids do have a fixed volume; it is gases that have neither fixed shape nor fixed volume.
📌 SSC & Railway Exam Facts
• Rate of diffusion: gases > liquids > solids.
• Liquids: definite volume, no definite shape; gases: neither.
• Diffusion becomes faster on heating because the kinetic energy of the particles rises.
• Compressibility order: gases > liquids > solids; density order: solids > liquids > gases.
• Gases diffuse fastest because of the largest intermolecular space and negligible force of attraction.
RRB Technician Grade III 2024-25 – 23 December 2024 Shift 2 · States of matter and their properties

Q74. What is the primary difference between the particles of a solid and those of a gas?

  1. (a) Solid particles are made of different elements than gas particles.
  2. (b) Solid particles have more energy than gas particles.
  3. (c) Solid particles move more freely than gas particles.
  4. (d) Solid particles are more closely packed than gas particles.
Answer & solution

Answer: (d) Solid particles are more closely packed than gas particles.

Correct Answer: Option 4 — Solid particles are more closely packed than gas particles
The states of matter differ not in the kind of particles but in the arrangement, spacing and energy of those particles.
In a solid, the interparticle force of attraction is maximum and the interparticle space is minimum, so the particles are very closely packed in a regular pattern and can only vibrate about fixed positions. That is why solids have a definite shape, a definite volume, high density and are almost incompressible.
In a gas, the force of attraction is negligible and the interparticle space is enormous, so the particles move about randomly at high speed, filling the whole container. Hence gases have neither definite shape nor definite volume and are highly compressible — the very property that lets LPG and CNG be packed into cylinders.
❌ Why the other options are incorrect
✗ Solid particles are made of different elements than gas particles — the same substance can exist in all three states; ice, water and steam are all H₂O.
✗ Solid particles have more energy than gas particles — the kinetic energy order is gas > liquid > solid; solid particles have the least.
✗ Solid particles move more freely than gas particles — exactly the reverse; solid particles only vibrate, gas particles move freely.
📌 SSC & Railway Exam Facts
• Interparticle force: solid > liquid > gas; interparticle space: gas > liquid > solid.
• Kinetic energy of particles: gas > liquid > solid.
• Solid → definite shape and volume; liquid → definite volume only; gas → neither.
• Plasma and Bose–Einstein Condensate (BEC) are the fourth and fifth states of matter.
• BEC was predicted by S. N. Bose and Albert Einstein.
RRB Technician Grade III 2024-25 – 23 December 2024 Shift 2 · Evaporation and its factors

Q75. Cotton clothes are preferred in the summer season because ________.

  1. (a) cotton helps in absorbing water and exposes the sweat to the atmosphere for evaporation
  2. (b) cotton cannot expose the sweat to the atmosphere for evaporation
  3. (c) cotton does not absorb sweat
  4. (d) cotton is not helpful in absorbing water and exposes the sweat to the atmosphere for evaporation
Answer & solution

Answer: (a) cotton helps in absorbing water and exposes the sweat to the atmosphere for evaporation

Correct Answer: Option 1 — cotton helps in absorbing water and exposes the sweat to the atmosphere for evaporation
In summer the body cools itself by sweating. Evaporation is a surface phenomenon in which the faster-moving particles of a liquid escape into the air. To do so they take latent heat from the surroundings, so the surface left behind — here, our skin — is cooled. This is called evaporation causing cooling.
Cotton is a good absorber of water. It soaks the sweat from the skin and, being a porous fabric, spreads it over a large surface exposed to the atmosphere. The sweat then evaporates quickly, drawing latent heat of vaporisation from the body and giving a pleasant cooling effect. Synthetic cloth such as nylon or polyester neither absorbs sweat well nor lets it evaporate, so it feels sticky and hot.
❌ Why the other options are incorrect
✗ cotton cannot expose the sweat to the atmosphere for evaporation — the opposite is true; cotton's porous structure is precisely what exposes sweat to air.
✗ cotton does not absorb sweat — cotton is one of the best absorbers of water among common fabrics.
✗ cotton is not helpful in absorbing water and exposes the sweat... — half right only; it wrongly denies cotton's absorbing power, which is the first step of the cooling process.
📌 SSC & Railway Exam Facts
• Evaporation occurs at all temperatures and only at the surface; boiling occurs at a fixed temperature throughout the liquid.
• Evaporation increases with higher temperature, larger surface area, more wind and lower humidity.
• Evaporation causes cooling because of the absorption of latent heat of vaporisation.
• Water kept in an earthen pot (matka) cools by evaporation through its pores.
• Latent heat of vaporisation of water = 22.5 × 10⁵ J/kg; latent heat of fusion of ice = 3.34 × 10⁵ J/kg.
RRB Technician Grade III 2024-25 – 23 December 2024 Shift 3 · States of matter and their properties

Q76. Which of the following substances experiences the least change in shape when subjected to a change in pressure?

  1. (a) Solid
  2. (b) Gas
  3. (c) Plasma
  4. (d) Liquid
Answer & solution

Answer: (a) Solid

Correct Answer: Option 1 — Solid
How much a substance changes when pressure is applied depends on its compressibility, and compressibility depends on the space between the particles.
In a solid the particles are packed extremely close together and the force of attraction between them is maximum. There is almost no empty space to squeeze out, so a solid is practically incompressible and keeps its definite shape and definite volume even under large pressure. That rigidity is exactly why a solid shows the least change in shape.
In contrast, gases have huge interparticle spaces and are highly compressible — this is what allows large volumes of LPG and CNG to be stored in small cylinders, and oxygen to be compressed for hospital cylinders.
The order of compressibility is gases > liquids > solids.
❌ Why the other options are incorrect
✗ Gas — a gas is the most compressible state; it has neither fixed shape nor fixed volume, so it changes the most.
✗ Plasma — plasma is an ionised gas (the fourth state of matter); like a gas it has no definite shape at all.
✗ Liquid — a liquid has a fixed volume but no fixed shape; it flows and takes the shape of its container.
📌 SSC & Railway Exam Facts
• Compressibility: gas > liquid > solid; rigidity: solid > liquid > gas.
• Interparticle force: solid > liquid > gas; interparticle space: gas > liquid > solid.
• Plasma is the fourth state of matter — found in the sun, stars, neon signs and fluorescent tubes.
• BEC (Bose–Einstein Condensate) is the fifth state, formed at temperatures near absolute zero (0 K).
• Absolute zero = 0 K = −273.15 °C; K = °C + 273.
RRB Technician Grade III 2024-25 – 23 December 2024 Shift 3 · Interconversion of states (melting, boiling, sublimation, deposition)

Q77. Solid CO₂ gets converted directly into gaseous state on decrease of pressure to:

  1. (a) 10 atmosphere
  2. (b) 20 atmosphere
  3. (c) 1 atmosphere
  4. (d) 5 atmosphere
Answer & solution

Answer: (c) 1 atmosphere

Correct Answer: Option 3 — 1 atmosphere
Solid carbon dioxide (CO₂) is stored under high pressure. When the pressure is decreased to 1 atmosphere, the solid changes directly into carbon dioxide gas without ever becoming a liquid. A change of state from solid directly to gas (or gas directly to solid) is called sublimation.
Because it leaves no liquid residue — no wetness at all — solid CO₂ is popularly called dry ice. It sublimes at about −78 °C, which makes it an excellent refrigerant for storing ice cream, frozen food, blood and vaccines, and it is also used to create artificial smoke effects on stage.
This behaviour also shows how state depends on both pressure and temperature: increasing pressure brings particles closer, decreasing pressure lets them fly apart.
❌ Why the other options are incorrect
✗ 10 atmosphere — CO₂ is still held as a solid/liquid at such raised pressure; direct conversion to gas has not yet taken place.
✗ 20 atmosphere — even higher pressure keeps the particles tightly packed; this is closer to the storage pressure, not the subliming pressure.
✗ 5 atmosphere — still above normal atmospheric pressure; the change described happens only when pressure falls to the ordinary 1 atm.
📌 SSC & Railway Exam Facts
• Solid CO₂ = dry ice; it sublimes at about −78 °C at 1 atm.
• Other subliming solids: camphor, naphthalene, ammonium chloride (NH₄Cl) and iodine.
• Sublimation is used to separate a sublimable solid from a non-sublimable one, e.g. NH₄Cl from common salt.
• CO₂ is used in fire extinguishers and in aerated drinks; it is also a major greenhouse gas.
• State of matter depends on temperature and pressure; increasing pressure can turn a gas into a liquid.
RRB Technician Grade III 2024-25 – 20 December 2024 Shift 2 · States of matter and their properties

Q78. Which of the following is the characteristic of a liquid?

  1. (a) It has fixed volume but not fixed shape.
  2. (b) It is hard.
  3. (c) It has fixed shape and volume.
  4. (d) It is highly compressible.
Answer & solution

Answer: (a) It has fixed volume but not fixed shape.

Correct Answer: Option 1 — It has fixed volume but not fixed shape.
Matter exists in three common states — solid, liquid and gas — and the state is decided by the intermolecular force of attraction and the intermolecular space between its particles.
In a liquid the particles are held by moderate forces of attraction: strong enough to keep the particles together, so the volume stays fixed, but weak enough to let them slide over one another, so the liquid flows and takes the shape of its container. That is why 1 litre of water remains 1 litre whether it is poured into a bottle, a beaker or a bowl.
Liquids are also only slightly compressible, have densities lower than solids but far higher than gases, and show moderate diffusion — which is why gases dissolve in them (fish breathe the oxygen dissolved in water).
❌ Why the other options are incorrect
✗ It is hard — rigidity and hardness belong to solids, whose particles only vibrate about fixed positions and cannot flow.
✗ It has fixed shape and volume — this is the definition of a solid, not of a liquid.
✗ It is highly compressible — high compressibility belongs to gases, which have very large intermolecular spaces; that is why LPG and CNG can be compressed into cylinders.
📌 SSC & Railway Exam Facts
• Intermolecular force: solid > liquid > gas; intermolecular space and compressibility: gas > liquid > solid.
• Rate of diffusion: gas > liquid > solid.
• Fixed volume, no fixed shape → liquid; fixed shape and volume → solid; neither fixed → gas.
• Plasma and Bose–Einstein condensate (BEC) are the fourth and fifth states of matter.
• Liquids have fluidity, so both liquids and gases are together called fluids.
RRB Technician Grade III 2024-25 – 20 December 2024 Shift 2 · Evaporation and its factors

Q79. Which of the options provides the correct explanation for the following statement?
Sweating cools down your body on a hot day.

  1. (a) The given statement is wrong.
  2. (b) Sweating increases blood circulation and cools the body.
  3. (c) Sweating increases the body's temperature.
  4. (d) Sweating causes rapid evaporation, which absorbs heat from the body surface and cools the body.
Answer & solution

Answer: (d) Sweating causes rapid evaporation, which absorbs heat from the body surface and cools the body.

Correct Answer: Option 4 — Sweating causes rapid evaporation, which absorbs heat from the body surface and cools the body.
Evaporation is the change of a liquid into vapour at any temperature below its boiling point, and it takes place only from the surface of the liquid. The particles that escape are those with the highest kinetic energy, and to escape they must absorb energy — the latent heat of vaporisation — from their surroundings.
On a hot day the skin releases sweat, which is mostly water. As this sweat evaporates, it takes the latent heat it needs from the body surface, leaving the skin cooler. This is known as cooling caused by evaporation.
Evaporation becomes faster with higher temperature, larger surface area, greater wind speed and lower humidity — which is exactly why sweating cools us poorly on a humid day and very well on a dry, windy one.
❌ Why the other options are incorrect
✗ The given statement is wrong — the statement is scientifically correct; sweating genuinely lowers body temperature.
✗ Sweating increases blood circulation and cools the body — the cooling comes from the evaporation of sweat, not from any change in blood circulation.
✗ Sweating increases the body's temperature — exactly the opposite happens; evaporation removes heat and lowers the temperature of the skin.
📌 SSC & Railway Exam Facts
• Latent heat of vaporisation of water = 22.5 × 10⁵ J/kg (2260 kJ/kg); latent heat of fusion of ice = 3.34 × 10⁵ J/kg.
• Water stays cool in an earthen pot (matka) because water evaporating through its pores takes latent heat from the pot.
• Cotton clothes are worn in summer because cotton absorbs sweat and spreads it for fast evaporation.
• Evaporation is a surface phenomenon and a cooling process; boiling happens throughout the liquid at a fixed temperature.
• Evaporation increases with temperature, surface area and wind speed, and decreases with humidity.
RRB Technician Grade III 2024-25 – 20 December 2024 Shift 3 · Evaporation and its factors

Q80. What will be the effect of surface area on the evaporation process?

  1. (a) Evaporation increases with decrease in surface area.
  2. (b) Evaporation decreases with increase in surface area.
  3. (c) No effect of surface area on evaporation process.
  4. (d) Evaporation increases with increase in surface area.
Answer & solution

Answer: (d) Evaporation increases with increase in surface area.

Correct Answer: Option 4 — Evaporation increases with increase in surface area.
Evaporation is a surface phenomenon: only those particles that lie at the surface of the liquid and happen to possess enough kinetic energy can break free of the attraction of their neighbours and escape as vapour.
If the surface area is increased, a larger number of particles are exposed at the surface at any moment, so more of them get a chance to escape every second. Hence the rate of evaporation is directly proportional to the surface area. This is exactly why wet clothes dry faster when spread out than when left in a heap, and why hot tea cools faster when poured into a saucer.
The four factors controlling evaporation are temperature, surface area and wind speed (all directly proportional) and humidity (inversely proportional).
❌ Why the other options are incorrect
✗ Evaporation increases with decrease in surface area — the exact reverse of the truth; a smaller surface exposes fewer particles and slows evaporation.
✗ Evaporation decreases with increase in surface area — again reversed; enlarging the exposed surface always speeds up evaporation.
✗ No effect of surface area on evaporation process — surface area is one of the four main factors; since evaporation happens only at the surface, it can never be independent of surface area.
📌 SSC & Railway Exam Facts
• Rate of evaporation ∝ temperature, ∝ surface area, ∝ wind speed, and ∝ 1/humidity.
• Evaporation is a cooling process — the escaping particles take the latent heat of vaporisation from the surroundings.
• Evaporation occurs at every temperature and only at the surface; boiling occurs at a fixed temperature throughout the liquid.
• Water stays cool in an earthen pot because it evaporates through the pot's pores.
• On a humid day clothes dry slowly, because the surrounding air already holds a lot of water vapour.

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