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Acids, Bases and Salts PYQs – Chemistry, SSC & Railway

172 Acids, Bases and Salts (Chemistry) questions asked in recent SSC and Railway exams, newest first, with exam, date & shift, answers and solutions.

📚 172 questionsSSC 9 · Railway 163
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RRB Group D 2025-26 – 25 August 2026 Shift 1 · Neutralisation reaction

Q1. Which substance would best help neutralize the burning sensation caused by a bee sting containing methanoic acid?

  1. (a) Mild vinegar solution
  2. (b) Tamarind solution
  3. (c) Lemon juice
  4. (d) Mild baking soda solution
Answer & solution

Answer: (d) Mild baking soda solution

Correct Answer:
Correct Answer: Option 4 – Mild baking soda solution
Explanation:
A bee sting injectsmethanoic acid (formic acid), which causes the burning/painful sensation. To neutralize an acid, a mild base is needed.Baking soda (sodium bicarbonate)is a mild base and reacts with the acid, neutralizing it and relieving the pain.
Important Facts:
• Vinegar, tamarind, and lemon juice are all acidic and would worsen the burning sensation.
• Ant bites also inject formic acid and are treated the same way.
• Neutralization: acid + base → salt + water.
RRB Group D 2025-26 – 25 August 2026 Shift 1 · Nature of salts (acidic, basic, neutral)

Q2. A salt solution has a pH of 9. Which type of salt is it most likely to be?

  1. (a) Formed from a strong base and weak acid
  2. (b) Formed from a strong acid and weak base
  3. (c) Formed from a strong acid and strong base
  4. (d) Formed from a weak acid and weak base
Answer & solution

Answer: (a) Formed from a strong base and weak acid

Correct Answer:
Correct Answer: Option 1 – Formed from a strong base and weak acid
Explanation:
A salt solution withpH 9is basic in nature (pH > 7). Salts formed from astrong base and a weak acidhydrolyze in water to give a basic solution (e.g., sodium acetate, sodium carbonate), consistent with a pH of 9.
Important Facts:
• Salts of strong acid + weak base give acidic solutions (pH < 7), e.g., ammonium chloride.
• Salts of strong acid + strong base are neutral (pH = 7), e.g., sodium chloride.
• Salts of weak acid + weak base give solutions near neutral, depending on relative strengths.
RRB Group D 2025-26 – 25 August 2026 Shift 2 · Properties of bases and alkalis

Q3. Which of these statements best describes why non-metallic oxides react with bases?

  1. (a) They behave as acidic oxides and neutralize bases
  2. (b) They form acids and bases together
  3. (c) They are always basic and do not react with bases
  4. (d) They behave as basic oxides and neutralize acids
Answer & solution

Answer: (a) They behave as acidic oxides and neutralize bases

Correct Answer:
Correct Answer: Option 1 – They behave as acidic oxides and neutralize bases
Explanation:
Non-metallic oxides (e.g., CO₂, SO₂) are generallyacidic in nature. When they react with a base, they behave as acidic oxides and undergo neutralization, forming salt and water — analogous to how an acid reacts with a base. For example: CO₂ + Ca(OH)₂ → CaCO₃ + H₂O.
RRB Group D 2025-26 – 25 August 2026 Shift 3 · Properties of acids

Q4. How are acids and bases similar in terms of their effect on skin?

  1. (a) They both can cause irritation or burns
  2. (b) They both clean the skin without harm
  3. (c) They both soothe the skin
  4. (d) They both act as moisturizers
Answer & solution

Answer: (a) They both can cause irritation or burns

Correct Answer:
Correct Answer: Option 1 – They both can cause irritation or burns
Explanation:
Strong acids and strong bases are both corrosive and can damage skin tissue, causing irritation, burns, or chemical damage on contact, though through different chemical mechanisms.
Important Facts:
• Strong acids (e.g., sulphuric acid) cause acid burns.
• Strong bases (e.g., sodium hydroxide) cause alkali burns, often felt as a slippery, soapy sensation.
• This is why safety precautions like gloves are needed when handling either acids or bases.
RRB Group D 2025-26 – 21 August 2026 Shift 1 · pH scale and its importance

Q5. A student measures the pH of four liquids: lemon juice (2), soap solution (9), water (7), and vinegar (3). Which is the most basic?

  1. (a) Water (7)
  2. (b) Vinegar (3)
  3. (c) Lemon juice (2)
  4. (d) Soap solution (9)
Answer & solution

Answer: (d) Soap solution (9)

Explanation:
A pH value greater than 7 indicates a basic (alkaline) solution, and the higher the pH above 7, the more basic the solution. Among the given values — lemon juice (2, acidic), vinegar (3, acidic), water (7, neutral), soap solution (9, basic) — soap solution has the highest pH and is thus the most basic.
Correct Answer: Option 4 – Soap solution (9)
RRB Group D 2025-26 – 21 August 2026 Shift 2 · Properties of acids

Q6. A student adds hydrochloric acid to sodium hydrogen carbonate. Which observation confirms neutralization?

  1. (a) Effervescence
  2. (b) Precipitate forms
  3. (c) Color turns red
  4. (d) Temperature drops
Answer & solution

Answer: (a) Effervescence

Correct Answer:
Correct Answer: Option 1 – Effervescence
Explanation:
NaHCO₃ + HCl → NaCl + H₂O + CO₂. The reaction between the acid and sodium hydrogen carbonate releases carbon dioxide gas, seen as brisk bubbling (effervescence). This gas evolution is the observable confirmation that the acid has reacted completely with the base/salt.
Important Facts:
• No precipitate forms since both NaCl and the by-products are soluble.
• The reaction is mildly exothermic but does not produce a dramatic colour change.
RRB Group D 2025-26 – 21 August 2026 Shift 2 · Properties of bases and alkalis

Q7. When carbon dioxide (CO₂) reacts with sodium hydroxide (NaOH), the salt formed is:

  1. (a) sodium chloride
  2. (b) sodium sulphate
  3. (c) sodium carbonate
  4. (d) sodium nitrate
Answer & solution

Answer: (c) sodium carbonate

Correct Answer:
Correct Answer: Option 3 – sodium carbonate
Explanation:
CO₂ + 2NaOH → Na₂CO₃ + H₂O. Carbon dioxide, being an acidic oxide, reacts with the base sodium hydroxide to form sodium carbonate and water.
RRB Group D 2025-26 – 21 August 2026 Shift 3 · Common salts - preparation and uses (baking soda, washing soda, bleaching powder, plaster of Paris)

Q8. Which of the following is NOT a use of bleaching powder?

  1. (a) Manufacturing chloroform
  2. (b) Bleaching cotton and linen
  3. (c) Removing hardness of water
  4. (d) Disinfecting drinking water
Answer & solution

Answer: (c) Removing hardness of water

Correct Answer:
Correct Answer: Option 3 – Removing hardness of water
Explanation:
Bleaching powder is used for bleaching cotton/linen, disinfecting drinking water, and in the manufacture of chloroform.Removing hardness of wateris NOT its use — that is done using washing soda (sodium carbonate) or ion-exchange methods.
Important Facts:
• Bleaching powder, Ca(OCl)Cl, is also used as an oxidising agent in various chemical industries.
RRB Group D 2025-26 – 21 August 2026 Shift 3 · Neutralisation reaction

Q9. Which products are always formed during a complete neutralization chemical reaction?

  1. (a) Acid and base
  2. (b) Metal and gas
  3. (c) Salt and water
  4. (d) Gas and salt
Answer & solution

Answer: (c) Salt and water

Correct Answer:
Correct Answer: Option 3 – Salt and water
Explanation:
A complete neutralization reaction is: Acid + Base →Salt + Water. This is always the pattern regardless of the specific acid or base involved.
Important Facts:
• Example: HCl + NaOH → NaCl + H2O.
RRB Group D 2025-26 – 20 August 2026 Shift 1 · Neutralisation reaction

Q10. Consider the reaction: HCl(aq) + NaOH(aq) → NaCl(aq) + H₂O(l)This reaction is best classified as which type of chemical reactions?

  1. (a) Decomposition reaction
  2. (b) Displacement reaction
  3. (c) Combination reaction
  4. (d) Neutralization reaction
Answer & solution

Answer: (d) Neutralization reaction

Correct Answer:
Correct Answer: Option 4 – Neutralization reaction
Explanation:
HCl (an acid) reacts with NaOH (a base) to form NaCl (a salt) and H₂O (water). A reaction between an acid and a base to produce salt and water is called aneutralization reaction.
Important Facts:
• General form: Acid + Base → Salt + Water.
• Neutralization reactions are typically exothermic.
RRB Group D 2025-26 – 20 August 2026 Shift 1 · Properties of acids

Q11. Which gas is usually released when acid reacts with metals?

  1. (a) nitrogen
  2. (b) carbon dioxide
  3. (c) hydrogen
  4. (d) chlorine
Answer & solution

Answer: (c) hydrogen

Correct Answer:
Correct Answer: Option 3 – hydrogen
Explanation:
When a reactive metal reacts with a dilute acid, it displaceshydrogen gas
, which can be tested with a burning splint producing a characteristic 'pop' sound.Example: Zn + 2HCl → ZnCl₂ + H₂↑
Important Facts:
• Metal + Dilute Acid → Salt + Hydrogen gas.
• This does not occur with unreactive metals like copper and dilute acids under normal conditions.
RRB Group D 2025-26 – 20 August 2026 Shift 2 · Neutralisation reaction

Q12. A reaction between an acid and a base produces:

  1. (a) Hydrogen gas and metal
  2. (b) Only water
  3. (c) Only salt
  4. (d) Salt and water
Answer & solution

Answer: (d) Salt and water

Correct Answer:
Correct Answer: Option 4 – Salt and water
Explanation:
An acid–base (neutralisation) reaction produces a salt and water, e.g., HCl + NaOH → NaCl + H₂O.
Important Facts:
• Hydrogen gas and a salt are produced when an acid reacts with a reactive metal, not a base.
RRB Group D 2025-26 – 20 August 2026 Shift 3 · Common salts - preparation and uses (baking soda, washing soda, bleaching powder, plaster of Paris)

Q13. When Plaster of Paris (CaSO₄·½H₂O) is mixed with water, it becomes hard. Which process is responsible for this hardening?

  1. (a) Rehydration to form gypsum
  2. (b) Dehydration of calcium sulphate
  3. (c) Neutralization between acid and base
  4. (d) Oxidation of calcium ions
Answer & solution

Answer: (a) Rehydration to form gypsum

Correct Answer:
Option 1 – Rehydration to form gypsum
Explanation:
When Plaster of Paris (CaSO₄·½H₂O) is mixed with water, it absorbs water molecules and gets converted back to gypsum (CaSO₄·2H₂O), a hard, crystalline solid. Thisrehydrationreaction is responsible for the setting/hardening of Plaster of Paris.
RRB Group D 2025-26 – 19 August 2026 Shift 1 · pH scale and its importance

Q14. Which pH range is best for most plants to grow in garden soil?

  1. (a) Between pH 6 and pH 7.5
  2. (b) Between pH 4 and pH 5
  3. (c) Between pH 8.5 and pH 9.5
  4. (d) Between pH 3 and pH 4
Answer & solution

Answer: (a) Between pH 6 and pH 7.5

Correct Answer:
Correct Answer: Option 1 – Between pH 6 and pH 7.5
Explanation:
Most garden plants grow best inslightly acidic to neutral soil, typically in thepH range of 6 to 7.5, as this range allows optimal availability of essential nutrients to plant roots.
Important Facts:
• Very acidic (pH 3-5) or very alkaline (pH 8.5-9.5) soils can limit nutrient uptake and harm most plants.
• Some specific plants (e.g., blueberries) prefer more acidic soil, but this is an exception, not the general rule.
RRB Group D 2025-26 – 19 August 2026 Shift 2 · Common salts - preparation and uses (baking soda, washing soda, bleaching powder, plaster of Paris)

Q15. Which of the following is a product formed at the cathode during the electrolysis of brine?

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

Answer: (b) Hydrogen gas

Correct Answer:
Correct Answer: Option 2 – Hydrogen gas
Explanation:
During electrolysis of brine (concentrated aqueous NaCl solution), at thecathode, water molecules are preferentially reduced (since Na⁺ is not easily reduced in aqueous solution), releasinghydrogen gas (H₂)and leaving OH⁻ ions behind (forming NaOH in solution). At theanode, Cl⁻ ions are oxidized to releasechlorine gas (Cl₂).
Important Facts:
• Chlor-alkali process: 2NaCl + 2H₂O → 2NaOH + H₂ (cathode) + Cl₂ (anode).
• Products: H₂ gas, Cl₂ gas, and NaOH solution — all industrially important.
RRB Group D 2025-26 – 19 August 2026 Shift 3 · Properties of bases and alkalis

Q16. A student mixes a non-metallic oxide with a base and observes neutralization. What does this suggest about the properties of the substances involved?

  1. (a) The non-metallic oxide acts as an acid
  2. (b) The non-metallic oxide acts as a base
  3. (c) Both substances are neutral
  4. (d) The base acts as an acid
Answer & solution

Answer: (a) The non-metallic oxide acts as an acid

Correct Answer:
Option 1 – The non-metallic oxide acts as an acid
Explanation:
Neutralization occurs when anacid reacts with a baseto form salt and water. Since the non-metallic oxide neutralizes the base, it must be behaving as an acid. Non-metallic oxides (e.g., CO₂, SO₂) are generallyacidic oxides, in contrast to metallic oxides which are generally basic.
Important Facts:
• Metallic oxides are basic in nature (e.g., Na₂O, CaO).
• Non-metallic oxides are acidic in nature (e.g., CO₂ + H₂O → H₂CO₃).
• Some oxides (like ZnO, Al₂O₃) are amphoteric — react with both acids and bases.
Correct Answer: Option 1 – The non-metallic oxide acts as an acid
RRB Group D 2025-26 – 18 August 2026 Shift 1 · Common salts - preparation and uses (baking soda, washing soda, bleaching powder, plaster of Paris)

Q17. A doctor is preparing a cast for a fractured arm. Why is Plaster of Paris preferred over cement or lime for this purpose?

  1. (a) It is more colorful
  2. (b) It is heavier than cement
  3. (c) It produces heat when mixed with water
  4. (d) It sets quickly and forms a hard, supportive mass
Answer & solution

Answer: (d) It sets quickly and forms a hard, supportive mass

Plaster of Paris for casts
Plaster of Paris (calcium sulphate hemihydrate) when mixed with water sets quickly into a hard, solid mass (gypsum), forming a rigid support that conforms to the shape of the limb before hardening.
This quick-setting, hardening property makes it ideal for supporting a fractured bone, unlike cement or lime which set too slowly or are unsuitable for direct skin contact.
Correct Answer: It sets quickly and forms a hard, supportive mass
RRB Group D 2025-26 – 18 August 2026 Shift 2 · Indicators (natural, synthetic, olfactory)

Q18. What is the reason for the colour change of phenolphthalein after adding an acid to a basic solution?

  1. (a) The solution is diluted
  2. (b) The solution becomes neutral or acidic
  3. (c) The temperature increases
  4. (d) The solution evaporates
Answer & solution

Answer: (b) The solution becomes neutral or acidic

Phenolphthalein Colour Change
Phenolphthalein is pink in basic solutions and colourless in neutral or acidic solutions.
When acid is added to a basic solution containing phenolphthalein, the acid neutralizes the base; as the solution becomes neutral (and then acidic with excess acid), the indicator turns colourless.
Correct Answer: The solution becomes neutral or acidic
RRB Group D 2025-26 – 18 August 2026 Shift 3 · Properties of bases and alkalis

Q19. What is a common observable change when a non-metallic oxide is bubbled through a base?

  1. (a) The temperature of the solution falls sharply
  2. (b) The solution turns bright red in color
  3. (c) A gas is evolved rapidly during the reaction
  4. (d) There is a decrease in alkalinity of the solution
Answer & solution

Answer: (d) There is a decrease in alkalinity of the solution

Concept: Reaction of a Non-Metallic Oxide with a Base
Non-metallic oxides (e.g., CO₂, SO₂) are acidic in nature. When such an acidic oxide is bubbled through a basic (alkaline) solution, it neutralizes some of the base, forming a salt (e.g., a carbonate) and water. As the base is consumed in this neutralization reaction, thealkalinity of the solution decreases.
There is no rapid evolution of gas (the gas is being absorbed, not released), no sharp temperature drop (neutralization is typically mildly exothermic), and no colour change to bright red under normal conditions.
Correct Answer: There is a decrease in alkalinity of the solution
RRB Group D 2025-26 – 17 August 2026 Shift 2 · Properties of acids

Q20. If a student mixes acetic acid with sodium hydroxide and observes bubbling, what might explain this observation?

  1. (a) A contaminant like carbonate is present
  2. (b) Water is forming as the only product
  3. (c) The reaction is very slow
  4. (d) The reaction is already complete
Answer & solution

Answer: (a) A contaminant like carbonate is present

Unexpected Bubbling in Acid-Base Reaction
Acetic acid reacting with sodium hydroxide is a simple neutralization reaction (acid + base → salt + water), which does not normally produce gas/bubbles. If bubbling is observed, it strongly suggestsa contaminant such as carbonate/bicarbonateis present in one of the reagents; carbonates react with acids to release CO₂ gas, causing effervescence.
• Water forming as the only product would not cause visible bubbling.
• A slow reaction or a completed reaction does not explain gas evolution.
Correct Answer: A contaminant like carbonate is present
RRB Group D 2025-26 – 17 August 2026 Shift 3 · Common salts - preparation and uses (baking soda, washing soda, bleaching powder, plaster of Paris)

Q21. Baking soda is commonly used in fire extinguishers because it releases a specific gas when heated. What is the gas released and how does it help extinguish fires?

  1. (a) It releases nitrogen, which cools the burning material
  2. (b) It releases sulfur dioxide, which reacts with the flames
  3. (c) It releases oxygen, which smothers the fire and prevents it from spreading
  4. (d) It releases carbon dioxide, which displaces oxygen and stops combustion
Answer & solution

Answer: (d) It releases carbon dioxide, which displaces oxygen and stops combustion

Baking Soda in Fire Extinguishers
Baking soda (sodium bicarbonate, NaHCO₃) decomposes on heating: 2NaHCO₃ → Na₂CO₃ + H₂O + CO₂.
• The reaction releasescarbon dioxide gas.
• CO₂ is heavier than air and non-combustible, so it forms a blanket over the fire, displacing/cutting off the oxygen supply and stopping combustion.
Correct Answer: It releases carbon dioxide, which displaces oxygen and stops combustion
RRB Group D 2025-26 – 17 August 2026 Shift 3 · Neutralisation reaction

Q22. When hydrochloric acid reacts with sodium hydroxide to form sodium chloride and water, which type of reaction is primarily demonstrated?

  1. (a) Double displacement reaction
  2. (b) Redox reaction
  3. (c) Displacement reaction
  4. (d) Combination reaction
Answer & solution

Answer: (a) Double displacement reaction

HCl and NaOH Reaction Type
HCl + NaOH → NaCl + H₂O
• This is an acid-base neutralisation reaction, which is a specific type ofdouble displacement reaction— the H⁺ ion from the acid and the Na⁺ ion from the base exchange partners (Cl⁻ and OH⁻).
• It is not a redox reaction (no change in oxidation states/electron transfer), not a simple displacement (no single element displacing another), and not a combination reaction (two compounds react to give two different compounds, not one).
Correct Answer: Double displacement reaction
RRB Group D 2025-26 – 14 August 2026 Shift 1 · Properties of acids

Q23. A student accidentally spills a small amount of dilute sulfuric acid on the laboratory table. The teacher suggests adding sodium bicarbonate powder to neutralize the acid.Which product confirms that a neutralization reaction has occurred?

  1. (a) Formation of oxygen gas
  2. (b) Formation of carbon dioxide and salt
  3. (c) Formation of hydrogen gas
  4. (d) Formation of metal oxide
Answer & solution

Answer: (b) Formation of carbon dioxide and salt

Answer: Option 2 – Formation of carbon dioxide and salt.
• Acid + sodium bicarbonate → salt + water +CO₂, confirming neutralisation (effervescence).
RRB Group D 2025-26 – 14 August 2026 Shift 1 · Properties of acids

Q24. Identify the correct statement regarding the reaction of sodium carbonate and dilute HCl.

  1. (a) Hydrogen is released.
  2. (b) Carbon dioxide is released.
  3. (c) Chlorine is released.
  4. (d) Carbon monoxide is released.
Answer & solution

Answer: (b) Carbon dioxide is released.

Answer: Option 2 – Carbon dioxide is released.
• Na₂CO₃ + 2HCl → 2NaCl + H₂O +CO₂.
RRB Group D 2025-26 – 14 August 2026 Shift 1 · Properties of acids

Q25. When a metal reacts with a dilute acid, hydrogen gas is released. What is the compound formed along with hydrogen gas called?

  1. (a) Water
  2. (b) Oxide
  3. (c) Base
  4. (d) Salt
Answer & solution

Answer: (d) Salt

Answer: Option 4 – Salt.
• Metal + acid →salt+ hydrogen gas.
RRB Group D 2025-26 – 14 August 2026 Shift 3 · Indicators (natural, synthetic, olfactory)

Q26. Methyl orange turns red in:

  1. (a) Both acid and base
  2. (b) Base only
  3. (c) Neutral solution
  4. (d) Acid only
Answer & solution

Answer: (d) Acid only

Answer: Option 4 – Acid only.
• Methyl orange turnsred in acidicsolution (yellow in base).
RRB Group D 2025-26 – 13 August 2026 Shift 2 · Common salts - preparation and uses (baking soda, washing soda, bleaching powder, plaster of Paris)

Q27. Which gas released from bleaching powder is primarily responsible for its bleaching and disinfecting action?

  1. (a) Chlorine (Cl₂)
  2. (b) Carbon dioxide (CO₂)
  3. (c) Hydrogen chloride (HCl)
  4. (d) Oxygen (O₂)
Answer & solution

Answer: (a) Chlorine (Cl₂)

Answer: Option 1 – Chlorine (Cl₂).
• Bleaching powder releaseschlorine, responsible for bleaching and disinfecting.
RRB Group D 2025-26 – 13 August 2026 Shift 3 · Neutralisation reaction

Q28. Read the following statements carefully and choose the CORRECT option:S̲t̲a̲t̲e̲m̲e̲n̲t̲ ̲I̲:̲ Neutralisation reactions always produce salt, water, and hydrogen gas.S̲t̲a̲t̲e̲m̲e̲n̲t̲ ̲I̲I̲:̲ Neutralisation reaction is a type of double displacement reaction.

  1. (a) Only Statement II is correct
  2. (b) Only Statement I is correct
  3. (c) Both statements are correct
  4. (d) Both statements are incorrect
Answer & solution

Answer: (a) Only Statement II is correct

Answer: Option 1 – Only Statement II is correct.
• Neutralisation gives salt + water (not hydrogen gas), so Statement I is wrong; it is adouble displacementreaction (Statement II correct).
RRB Group D 2025-26 – 12 August 2026 Shift 1 · Properties of acids

Q29. Why should acids be diluted carefully?

  1. (a) To avoid splashing
  2. (b) To make reaction fast
  3. (c) To increase acidity
  4. (d) To reduce concentration
Answer & solution

Answer: (a) To avoid splashing

Answer: Option 1 – To avoid splashing.
• Acid is added to water slowly because the reaction is highly exothermic; thisprevents splashingof hot acid.
RRB Group D 2025-26 – 12 August 2026 Shift 3 · Common salts - preparation and uses (baking soda, washing soda, bleaching powder, plaster of Paris)

Q30. Sodium carbonate (washing soda) is used in which of the following industries?a. glassb. soapc. paper

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

Answer: (b) a, b and c

Answer: Option 2 – a, b and c.
• Washing soda (Na₂CO₃) is used inglass, soap and paperindustries.
RRB Group D 2025-26 – 11 August 2026 Shift 1 · Properties of bases and alkalis

Q31. When sodium hydroxide is dissolved in water, which type of ions are mainly responsible for making the solution basic?

  1. (a) Hydrogen ions (H⁺)
  2. (b) Hydroxide ions (OH⁻)
  3. (c) Sodium ions (Na⁺)
  4. (d) Carbonate ions (CO₃²⁻)
Answer & solution

Answer: (b) Hydroxide ions (OH⁻)

Answer: Option 2 – Hydroxide ions (OH⁻).
• NaOH → Na⁺ + OH⁻. TheOH⁻ ionsmake the solution basic (alkaline).
RRB Group D 2025-26 – 11 August 2026 Shift 2 · Properties of acids

Q32. Different acids show similar chemical properties because they all produce which of the following ions in aqueous solution?

  1. (a) Chlorine ions
  2. (b) Sodium ions
  3. (c) Hydrogen ions
  4. (d) Hydroxide ions
Answer & solution

Answer: (c) Hydrogen ions

Answer: Option 3 – Hydrogen ions.
• All acids releaseH⁺ (H₃O⁺) ionsin aqueous solution, giving them common acidic properties.
RRB Group D 2025-26 – 11 August 2026 Shift 3 · Properties of acids

Q33. Both acids and bases conduct electricity in an aqueous solution because:

  1. (a) They contain free electrons
  2. (b) They produce ions in water
  3. (c) They form covalent bonds
  4. (d) They release oxygen gas
Answer & solution

Answer: (b) They produce ions in water

Answer: Option 2 – They produce ions in water.
• Acids and bases conduct electricity because theyionize in water, giving free-moving ions.
RRB Group D 2025-26 – 10 August 2026 Shift 1 · Properties of bases and alkalis

Q34. When a metal oxide reacts with an acid, it forms:

  1. (a) salt and water as final products
  2. (b) acid and metal oxide mixture only
  3. (c) carbon dioxide and hydrogen gas
  4. (d) salt and hydrogen gas evolution
Answer & solution

Answer: (a) salt and water as final products

Answer: Option 1 — salt and water as final products
Metal oxide (basic) + acid →salt + water→ Option 1.
RRB Group D 2025-26 – 10 August 2026 Shift 2 · Common salts - preparation and uses (baking soda, washing soda, bleaching powder, plaster of Paris)

Q35. During the preparation of baking soda in the laboratory, which gas is essential for its formation along with ammonia and water?

  1. (a) Nitrogen
  2. (b) Oxygen
  3. (c) Carbon dioxide
  4. (d) Hydrogen
Answer & solution

Answer: (c) Carbon dioxide

Answer: Option 3 – Carbon dioxide.
• Baking soda (NaHCO₃) is prepared in the Solvay process by passingCO₂andammoniainto brine: NaCl + NH₃ + CO₂ + H₂O → NaHCO₃ + NH₄Cl.
RRB Group D 2025-26 – 9 August 2026 Shift 1 · Properties of acids

Q36. Which common feature of hydrochloric acid and sodium hydroxide solutions explains both their ability to change the pH of water and to conduct electricity?

  1. (a) Both produce ions in aqueous solution.
  2. (b) Both have a pH less than 7.
  3. (c) Both turn blue litmus red.
  4. (d) Both have a sour taste.
Answer & solution

Answer: (a) Both produce ions in aqueous solution.

Answer: Option 1 — Both produce ions in aqueous solution
Both HCl and NaOHproduce ions in water, which changes pH and conducts electricity → Option 1.
RRB Group D 2025-26 – 9 August 2026 Shift 2 · Nature of salts (acidic, basic, neutral)

Q37. Salts of a strong acid and a strong base are generally:

  1. (a) amphoteric
  2. (b) basic
  3. (c) neutral
  4. (d) acidic
Answer & solution

Answer: (c) neutral

Answer: Option 3 — neutral
Salt of a strong acid + strong base isneutral(e.g., NaCl) → Option 3.
RRB Group D 2025-26 – 9 August 2026 Shift 3 · Properties of acids

Q38. Read the given statements of Assertion (A) and Reason (R) carefully and select the correct option.(A): Carbon dioxide gas is formed when acids react with metal carbonates.(R): Metal carbonates are basic in nature and neutralise acids to form salt, water and CO₂.

  1. (a) A is true, but R is false.
  2. (b) A is false, but R is true.
  3. (c) Both A and R are true, and R is the correct explanation of A
  4. (d) Both A and R are true, but R is not the correct explanation of A.
Answer & solution

Answer: (c) Both A and R are true, and R is the correct explanation of A

Answer: Option 3 — Both A and R true, R explains A
Acids + metal carbonates give CO₂ (A ✓); carbonates are basic and neutralise acids to give salt + water + CO₂ (R ✓, and it explains A) → Option 3.
RRB Group D 2025-26 – 6 August 2026 Shift 1 · Properties of bases and alkalis

Q39. Why do basic solutions conduct electricity when dissolved in water?

  1. (a) Hydroxide ions act as charge carriers
  2. (b) Heat energy produces electric current
  3. (c) Bases release free electrons
  4. (d) Bases dissolve completely without ions
Answer & solution

Answer: (a) Hydroxide ions act as charge carriers

Answer: Option 1 — Hydroxide ions act as charge carriers
Basic solutions conduct becauseOH⁻ ions(and cations) carry charge → Option 1.
RRB Group D 2025-26 – 6 August 2026 Shift 2 · Properties of acids

Q40. Which of the following correctly explains why an acid shows acidic behaviour only in aqueous solution?

  1. (a) Water prevents the ionisation of acids.
  2. (b) Hydrogen ions (H⁺) are produced only when the acid dissolves in water.
  3. (c) An acid loses H⁺ ions even in the absence of water.
  4. (d) The acid molecules remain completely ionised in the dry state.
Answer & solution

Answer: (b) Hydrogen ions (H⁺) are produced only when the acid dissolves in water.

Answer: Option 2 — H⁺ ions are produced only when the acid dissolves in water
An acid shows acidic behaviour only in water because itreleases H⁺ ions on dissolving→ Option 2.
RRB Group D 2025-26 – 6 August 2026 Shift 2 · Indicators (natural, synthetic, olfactory)

Q41. Clove oil is used as an olfactory indicator. If its smell persists in solution X but fades in solution Y, what can be inferred about the nature of the two solutions?

  1. (a) Both solutions X and Y are basic.
  2. (b) Solution X is basic and solution Y is acidic.
  3. (c) Both solutions X and Y are acidic.
  4. (d) Solution X is acidic and solution Y is basic.
Answer & solution

Answer: (d) Solution X is acidic and solution Y is basic.

Answer: Option 4 — Solution X is acidic and Y is basic
An olfactory indicator keeps its smell inacidand loses it inbase. Smell persists in X (acidic), fades in Y (basic) → Option 4.
RRB Group D 2025-26 – 6 August 2026 Shift 3 · pH scale and its importance

Q42. Which of the following solutions has the lowest hydrogen ion concentration?

  1. (a) Blood (pH = 7.4)
  2. (b) Vinegar (pH = 3)
  3. (c) Seawater (pH = 8.2)
  4. (d) Milk (pH = 6.6)
Answer & solution

Answer: (c) Seawater (pH = 8.2)

Answer: Option 3 — Seawater (pH = 8.2)
Higher pH = lower H⁺ concentration. Seawater (pH 8.2) has thelowest H⁺ concentration→ Option 3.
RRB Group D 2025-26 – 5 August 2026 Shift 1 · Properties of bases and alkalis

Q43. In the reaction of copper oxide with hydrochloric acid, the solution turns:

  1. (a) Blue-green due to copper(II) chloride
  2. (b) Brown due to hydrogen gas
  3. (c) Colourless due to water formation
  4. (d) Red due to oxygen evolution
Answer & solution

Answer: (a) Blue-green due to copper(II) chloride

Answer: Option 1 — Blue-green due to copper(II) chloride
CuO + 2HCl → CuCl₂ + H₂O.Copper(II) chloridegives the solution ablue-greencolour → Option 1.
RRB Group D 2025-26 – 5 August 2026 Shift 2 · Indicators (natural, synthetic, olfactory)

Q44. Which colour change does phenolphthalein show in a basic solution?

  1. (a) Blue to colourless instantly
  2. (b) Yellow to red immediately
  3. (c) White to green when shaken
  4. (d) Colourless to pink gradually
Answer & solution

Answer: (d) Colourless to pink gradually

Answer: Option 4 — Colourless to pink gradually
Phenolphthalein iscolourless in acid/neutraland turnspinkin a basic solution → Option 4.
RRB Group D 2025-26 – 5 August 2026 Shift 3 · Indicators (natural, synthetic, olfactory)

Q45. Which of the following is commonly used as an olfactory indicator?

  1. (a) Vanilla essence
  2. (b) Litmus
  3. (c) Methyl orange
  4. (d) Phenolphthalein
Answer & solution

Answer: (a) Vanilla essence

Answer: Option 1 — Vanilla essence
Anolfactory indicatorchanges smell in acid/base — e.g.,vanilla essence→ Option 1.
RRB Group D 2025-26 – 4 August 2026 Shift 1 · Properties of acids

Q46. Which gas is released when a dilute acid reacts with a metal carbonate?

  1. (a) Carbon dioxide gas is released
  2. (b) Oxygen gas is released
  3. (c) Nitrogen gas is released
  4. (d) Hydrogen gas is released
Answer & solution

Answer: (a) Carbon dioxide gas is released

Answer: Option 1 — Carbon dioxide gas is released
Acid + metal carbonate → salt + water +CO₂. (Acid + metal gives H₂; here it is a carbonate, so CO₂.) → Option 1.
RRB Group D 2025-26 – 4 August 2026 Shift 3 · Neutralisation reaction

Q47. If hydrochloric acid (HCl) reacts with sodium hydroxide (NaOH), which ions from each reactant participate in forming water?

  1. (a) H+(aq) from HCl and OH-(aq) from NaOH
  2. (b) H+(aq) from NaOH and OH-(aq) from HCl
  3. (c) Na+(aq) from NaOH and Cl-(aq) from HCl
  4. (d) Cl-(aq) from HCl and Na+(aq) from NaOH
Answer & solution

Answer: (a) H+(aq) from HCl and OH-(aq) from NaOH

Answer: Option 1 — H⁺ from HCl and OH⁻ from NaOH
Water forms fromH⁺ (from HCl) + OH⁻ (from NaOH) → H₂O→ Option 1.
RRB Group D 2025-26 – 3 August 2026 Shift 1 · Neutralisation reaction

Q48. When hydrochloric acid reacts with sodium hydroxide, what is formed as a result of the neutralization reaction?

  1. (a) Salt and water
  2. (b) Gas only
  3. (c) Base only
  4. (d) Acid only
Answer & solution

Answer: (a) Salt and water

Answer: Option 1 — Salt and water
Neutralisation:Acid + Base → Salt + Water.
HCl + NaOH → NaCl + H₂O →salt and water→ Option 1.
RRB Group D 2025-26 – 3 August 2026 Shift 2 · pH scale and its importance

Q49. A higher concentration of H+ ions in a solution corresponds to:

  1. (a) Constant pH
  2. (b) Higher pH value
  3. (c) Lower pH value
  4. (d) Neutral pH
Answer & solution

Answer: (c) Lower pH value

Answer: Option 3 — Lower pH value
pH = −log[H⁺]. Ahigher H⁺ concentrationmeans alower pH(more acidic) → Option 3.
RRB Group D 2025-26 – 3 August 2026 Shift 3 · Common salts - preparation and uses (baking soda, washing soda, bleaching powder, plaster of Paris)

Q50. Why is baking soda preferred over sodium carbonate in fire extinguishers?

  1. (a) It releases carbon dioxide easily with acid
  2. (b) It reacts violently producing heat
  3. (c) It forms insoluble residue
  4. (d) It produces hydrogen gas rapidly
Answer & solution

Answer: (a) It releases carbon dioxide easily with acid

Answer: Option 1 — It releases CO₂ easily with acid
Baking soda (NaHCO₃) reacts with acids toquickly release CO₂, which smothers the fire → Option 1.
RRB NTPC UG CBT-1 2025-26 – 19 June 2026 Shift 1 · Common salts - preparation and uses (baking soda, washing soda, bleaching powder, plaster of Paris)

Q51. When electricity is passed through an aqueous solution of sodium chloride (called brine), it decomposes to form sodium hydroxide. This process is called:

  1. (a) Polymerisation process
  2. (b) Sublimation process
  3. (c) Chlor-alkali process
  4. (d) Filtration process
Answer & solution

Answer: (c) Chlor-alkali process

Electrolysis of Brine (NaCl solution)
When electric current passes through aqueous NaCl:
At cathode: 2H₂O + 2e⁻ → H₂ + 2OH⁻
At anode: 2Cl⁻ → Cl₂ + 2e⁻
Products formed:
• Chlorine gas (Cl₂) at anode
• Hydrogen gas (H₂) at cathode
• Sodium hydroxide (NaOH) in solution
This process is called Chlor-alkali process
(Chlor = Chlorine, Alkali = NaOH)
Answer: Option 3 → Chlor-alkali process
RRB NTPC UG CBT-1 2025-26 – 19 June 2026 Shift 3 · Properties of acids

Q52. Since hydrogen ions cannot exist alone and exist only after combining with water molecules, they must always be shown as which among the following, represented as H₃O⁺?

  1. (a) Hydrogen gas
  2. (b) Oxide ion
  3. (c) Hydronium ion
  4. (d) Hydroxide ion
Answer & solution

Answer: (c) Hydronium ion

Hydrogen Ions in Aqueous Solution
H⁺ ions are highly reactive and cannot exist freely in water.
They immediately combine with water molecules:
H⁺ + H₂O → H₃O⁺
H₃O⁺ is called theHydronium ion.
This is the actual form of hydrogen ions in aqueous solutions.
Answer: Option 3 → Hydronium ion
RRB NTPC UG CBT-1 2025-26 – 15 June 2026 Shift 3 · pH scale and its importance

Q53. Which of the following substances is considered neutral according to the pH scale?

  1. (a) Sea water
  2. (b) Stomach acid
  3. (c) Lime juice
  4. (d) Pure water
Answer & solution

Answer: (d) Pure water

Topic: pH Scale and Neutrality
pH scale ranges from 0 to 14.
pH < 7 → Acidic, pH = 7 → Neutral, pH > 7 → Basic
Sea water: pH ≈ 8 (slightly basic)
Stomach acid: pH ≈ 1-2 (highly acidic)
Lime juice: pH ≈ 2-3 (acidic)
Pure water: pH = 7 (neutral)
Answer: Option 4 → Pure water
RRB NTPC UG CBT-1 2025-26 – 7 May 2026 Shift 3 · Properties of acids

Q54. When dilute Hydrochloric acid (HCl) reacts with Sodium Hydrogen Carbonte (NaHCO₃), which is the product formed along with Sodium chloride(NaCl) and Water(H₂O)?

  1. (a) Chloroform (CHCl3)
  2. (b) Carbon Dioxide(CO₂)
  3. (c) Ammonium Chloride (NH4Cl)
  4. (d) Hydrogen gas(H₂)
Answer & solution

Answer: (b) Carbon Dioxide(CO₂)

Topic:Acid-Base Reaction
Reaction: HCl + NaHCO₃ → NaCl + H₂O + ?
NaHCO₃ (sodium bicarbonate) is a weak base.
When acid reacts with carbonate/bicarbonate, CO₂ gas is released.
Complete equation:
HCl + NaHCO₃ → NaCl + H₂O + CO₂↑
Observation: Effervescence (bubbles) due to CO₂ gas.
Answer: Option 2 → Carbon Dioxide(CO₂)
RRB NTPC GL CBT-1 2025-26 – 24 March 2026 Shift 1 · Properties of acids

Q55. Which ion is responsible for the acidic nature of solutions?

  1. (a) Hydrogen ion (H+)
  2. (b) Chloride ion (Cl-)
  3. (c) Hydroxide ion (OH-)
  4. (d) Sodium ion (Na+)
Answer & solution

Answer: (a) Hydrogen ion (H+)

Acidic Nature of Solutions
Acids releaseH⁺ ions(hydrogen ions) when dissolved in water.
H⁺ ions are responsible for acidic properties like sour taste, turning blue litmus red, and pH < 7.
OH⁻ ions cause basic nature, while Cl⁻ and Na⁺ are neutral ions.
Answer: Option 1 → Hydrogen ion (H+)
RRB NTPC GL CBT-1 2025-26 – 18 March 2026 Shift 1 · Neutralisation reaction

Q56. Which option correctly completes the general word equation for a neutralisation reaction?
Base + Acid → ________ + ________

  1. (a) Salt +Carbon Dioxide
  2. (b) Metal +Water
  3. (c) Metal +Carbon Dioxide
  4. (d) Salt + Water
Answer & solution

Answer: (d) Salt + Water

Neutralisation Reaction
Definition: Reaction between acid and base
General equation:
Base + Acid → Salt + Water
Example: NaOH + HCl → NaCl + H₂O
Key point: Always produces salt and water
Answer: Option 4 → Salt + Water
RRB Technician Grade III 2025-26 – 10 March 2026 Shift 3 · pH scale and its importance

Q57. If the pH of a solution is 3, what is the concentration of hydrogen ions in the solution?

  1. (a) 1×10−2 M
  2. (b) 1×10−3 M
  3. (c) 3×10−2M
  4. (d) 3×10−3 M
Answer & solution

Answer: (b) 1×10−3 M

pH is defined as the negative logarithm of the hydrogen ion concentration.
pH = -log[H+]
Given pH = 3, so 3 = -log[H+]
log[H+] = -3
Therefore, [H+] = 10^(-3) M
Hence, the hydrogen ion concentration is 1×10^-3 M.
RRB Technician Grade III 2025-26 – 10 March 2026 Shift 2 · Indicators (natural, synthetic, olfactory)

Q58. Read the given statements carefully. Select which statement(s) is/are correct.
Statement-I: There are some substances whose odour changes in acidic or basic media. These are called olfactory indicators.
Statement-II: Vanilla extract and onion can be used as olfactory indicators.

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

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

Statement-I says that substances whose odour changes in acidic or basic media are called olfactory indicators, which is true.
Statement-II states that vanilla extract and onion can be used as olfactory indicators, which is also correct.
Therefore, both statements are correct. This topic relates to the use of olfactory indicators in chemistry for pH detection by smell change.
Hence, the correct answer is that both statements I and II are true.
RRB Technician Grade III 2025-26 – 10 March 2026 Shift 2 · Properties of acids

Q59. What is produced when an acid reacts with a metal hydrogen carbonate?

  1. (a) Salt, ammonia and water
  2. (b) Salt, oxygen and water
  3. (c) Salt, hydrogen gas and water
  4. (d) Salt, carbon dioxide and water
Answer & solution

Answer: (d) Salt, carbon dioxide and water

When an acid reacts with a metal hydrogen carbonate, the products are salt, carbon dioxide and water.
This reaction occurs because hydrogen carbonate decomposes releasing carbon dioxide and water, while the acid forms a salt with the metal.
Hence, the correct answer is salt, carbon dioxide and water.
RRB Technician Grade III 2025-26 – 10 March 2026 Shift 1 · pH scale and its importance

Q60. What is the concentration of H⁺ ions in pure water at 25°C ?

  1. (a) 1×10−1 M
  2. (b) 1×10−5 M
  3. (c) 1×10−4 M
  4. (d) 1×10−7 M
Answer & solution

Answer: (d) 1×10−7 M

The concentration of H⁺ ions in pure water at 25°C is 1×10⁻⁷ M.
This is because water self-ionises slightly, producing equal concentrations of H⁺ and OH⁻ ions as 10⁻⁷ M each.
This is a fundamental property used to define neutral pH as 7 at 25°C.
Hence, the correct concentration is 1×10⁻⁷ M.
RRB Technician Grade III 2025-26 – 10 March 2026 Shift 2 · Neutralisation reaction

Q61. Which of the following observations best confirms that a neutralisation reaction has occurred?

  1. (a) The solution changes from blue to red.
  2. (b) The pH of the solution becomes close to 7.
  3. (c) The temperature of the solution drops drastically.
  4. (d) A gas with a pungent smell is evolved.
Answer & solution

Answer: (b) The pH of the solution becomes close to 7.

Neutralisation reaction occurs between an acid and a base producing water and salt.
This reaction typically moves the solution's pH towards neutral, which is around 7.
Therefore, the best confirmation of neutralisation is that the pH of the solution becomes close to 7.
Other options do not reliably indicate neutralisation: colour change depends on the indicator; temperature may rise not drop; pungent gas is unrelated.
RRB Technician Grade III 2025-26 – 9 March 2026 Shift 2 · Indicators (natural, synthetic, olfactory)

Q62. What is the main advantage of using olfactory indicators?

  1. (a) They are useful for visually impaired individuals.
  2. (b) They give exact pH values.
  3. (c) They change colour sharply.
  4. (d) They can be used for all solutions.
Answer & solution

Answer: (a) They are useful for visually impaired individuals.

Olfactory indicators emit a specific smell to indicate pH changes.
They are especially useful for visually impaired individuals who cannot see colour changes.
This makes olfactory indicators practical for those relying on smell rather than sight in chemical testing.
Therefore, their main advantage is aiding visually impaired users.
RRB Technician Grade III 2025-26 – 9 March 2026 Shift 3 · pH scale and its importance

Q63. What will be the pH of a 0.01 M HCl solution?

  1. (a) 18
  2. (b) 8
  3. (c) 12
  4. (d) 2
Answer & solution

Answer: (d) 2

HCl is a strong acid which dissociates completely in aqueous solution.
So, concentration of H+ ions in 0.01 M HCl is 0.01 M.
pH = -log[H+] = -log(0.01)
= 2
Therefore, the pH of the solution is 2.
RRB Technician Grade III 2025-26 – 9 March 2026 Shift 1 · Neutralisation reaction

Q64. Which of the following are produced when a metal oxide reacts with an acid?

  1. (a) Salt and water
  2. (b) Salt and oxygen gas
  3. (c) Salt and carbon dioxide
  4. (d) Salt and hydrogen gas
Answer & solution

Answer: (a) Salt and water

When a metal oxide reacts with an acid, it undergoes a neutralisation reaction.
This reaction produces salt and water as products.
Metal oxide (basic oxide) + Acid → Salt + Water
Hence, the correct answer is salt and water.
RRB Technician Grade III 2025-26 – 6 March 2026 Shift 2 · Common salts - preparation and uses (baking soda, washing soda, bleaching powder, plaster of Paris)

Q65. In chemical industries, bleaching powder acts mainly as:

  1. (a) An oxidising agent
  2. (b) A reducing agent
  3. (c) A catalyst
  4. (d) A neutralising agent
Answer & solution

Answer: (a) An oxidising agent

Bleaching powder primarily releases chlorine, which can oxidise substances.
This makes it an effective oxidising agent in chemical industries.
Therefore, bleaching powder acts mainly as an oxidising agent.
Final answer: Option 1
RRB Technician Grade III 2025-26 – 6 March 2026 Shift 1 · pH scale and its importance

Q66. Which of the following correctly explains why toothpaste is basic in nature?

  1. (a) To lower the pH of saliva and prevent cavities
  2. (b) To provide an acidic medium for enzyme action in saliva
  3. (c) To react with water and release hydrogen ions
  4. (d) To neutralise the acid formed in the mouth after eating food
Answer & solution

Answer: (d) To neutralise the acid formed in the mouth after eating food

Option 4 is correct.
Toothpaste is basic because it neutralises the acid formed in the mouth after eating food.
The acid in the mouth can cause tooth decay, so neutralising it helps protect teeth.
This basic nature helps maintain oral hygiene and prevent cavities.
Hence, toothpaste contains ingredients that raise pH to counteract acids.
Final answer: Option 4
RRB Technician Grade III 2025-26 – 6 March 2026 Shift 3 · Common salts - preparation and uses (baking soda, washing soda, bleaching powder, plaster of Paris)

Q67. Which of the following is NOT a correct use or property of sodium hydrogen carbonate, NaHCO₃?

  1. (a) It is used as a strong acid.
  2. (b) It is used in fire extinguishers.
  3. (c) It is used in antacids.
  4. (d) It is used in baking as a leavening agent.
Answer & solution

Answer: (a) It is used as a strong acid.

Option 1 is correct because sodium hydrogen carbonate (NaHCO₃) is a weak base, not a strong acid.
Option 2 is true: it is used in dry chemical fire extinguishers due to its ability to release CO₂.
Option 3 is true: used in antacids to neutralise excess acid in the stomach.
Option 4 is true: used as a leavening agent in baking as it releases CO₂ when heated.
Hence, the only incorrect statement is that it is used as a strong acid.
Final answer: Option 1
RRB Technician Grade III 2025-26 – 6 March 2026 Shift 2 · Nature of salts (acidic, basic, neutral)

Q68. Which of the following salts, when dissolved in water, will produce a neutral solution?

  1. (a) Potassium hydroxide (KOH)
  2. (b) Sodium chloride (NaCl)
  3. (c) Sodium acetate (CH3COONa)
  4. (d) Ammonium chloride (NH4Cl)
Answer & solution

Answer: (b) Sodium chloride (NaCl)

Sodium chloride (NaCl) is formed from a strong acid (HCl) and a strong base (NaOH).
When dissolved, NaCl dissociates fully into Na+ and Cl- ions without hydrolysis.
No ions react with water to affect H+ or OH- concentration.
Therefore, the solution remains neutral.
Other salts like KOH (strong base), sodium acetate (from weak acid), and ammonium chloride (from weak base) change the pH.
Hence, NaCl produces a neutral solution.
Final answer: Option 2
RRB JE CBT-1 2025-26 – 20 February 2026 Shift 3 · Common salts - preparation and uses (baking soda, washing soda, bleaching powder, plaster of Paris)

Q69. Identify the CORRECT statement about the chlor-alkali process:

  1. (a) Sodium hydroxide is generated near the anode during electrolysis.
  2. (b) Hydrogen gas is formed at the cathode and chlorine gas at the anode.
  3. (c) It is used for the preparation of Na2CO3 solution by electrolysis of brine.
  4. (d) NaOH is formed at the anode and chlorine gas at the cathode.
Answer & solution

Answer: (b) Hydrogen gas is formed at the cathode and chlorine gas at the anode.

In the chlor-alkali process, brine (NaCl solution) is electrolysed.
At the cathode, hydrogen gas is produced by reduction of H+ ions.
At the anode, chlorine gas is produced by oxidation of chloride ions.
Sodium hydroxide (NaOH) is formed in the solution but not near the anode.
Hence, hydrogen gas forms at cathode and chlorine gas at anode is correct.
Final answer: Option 2
RRB JE CBT-1 2025-26 – 20 February 2026 Shift 3 · Common salts - preparation and uses (baking soda, washing soda, bleaching powder, plaster of Paris)

Q70. Washing soda is commonly used to:

  1. (a) Remove grease and soften water
  2. (b) Neutralise acids in human blood
  3. (c) Preserve meat for long periods
  4. (d) Increase acidity in baked foods
Answer & solution

Answer: (a) Remove grease and soften water

Washing soda is sodium carbonate decahydrate (Na2CO3·10H2O).
It is commonly used in households to remove grease stains from clothes and other surfaces.
It also softens hard water by removing calcium and magnesium ions.
Hence, the main use of washing soda is to remove grease and soften water.
Option 1 is correct.
Final answer: Option 1
RRB JE CBT-1 2025-26 – 20 February 2026 Shift 3 · Indicators (natural, synthetic, olfactory)

Q71. Which pair of olfactory indicators loses its smell in a basic solution?

  1. (a) Onion and blue litmus
  2. (b) Vanilla essence and clove oil
  3. (c) Phenolphthalein and onion
  4. (d) Turmeric and onion
Answer & solution

Answer: (b) Vanilla essence and clove oil

Option 2 is correct: Vanilla essence and clove oil lose their smell in a basic solution.
These compounds are sensitive to pH changes and typically lose their characteristic aroma in alkaline conditions.
Other options include substances that either are not primarily olfactory indicators or do not lose smell in base.
Hence, the correct answer is Vanilla essence and clove oil.
SSC MTS 2025 – 19 February 2026 Shift 3 · Common salts - preparation and uses (baking soda, washing soda, bleaching powder, plaster of Paris)

Q72. Which of the following is the use of chlorine gas?

  1. (a) Disinfectants
  2. (b) Soaps and detergents
  3. (c) Ammonia for fertilizers
  4. (d) De-greasing metals
Answer & solution

Answer: (a) Disinfectants

Correct Answer: Disinfectants (Option 1)
Chlorine gas is widely used as a disinfectant — in water treatment plants to kill bacteria and other harmful microorganisms, and in swimming pools to purify water.
Why other options are wrong:
Option 2 – Soaps and detergents are made using NaOH/KOH with fats and oils; chlorine is not used.
Option 3 – Ammonia for fertilizers is produced via the Haber-Bosch process (N₂ + H₂), not using chlorine.
Option 4 – De-greasing metals uses organic solvents, not chlorine gas.
RRB JE CBT-1 2025-26 – 19 February 2026 Shift 3 · Common salts - preparation and uses (baking soda, washing soda, bleaching powder, plaster of Paris)

Q73. Baking soda (NaHCO₃) is commonly used in cooking. Which of the following statements about it is correct?

  1. (a) It is acidic in nature and has pH < 7.
  2. (b) It reacts with acids to release carbon dioxide gas.
  3. (c) It does not react with water or acids.
  4. (d) It is a strong base that turns red litmus blue.
Answer & solution

Answer: (b) It reacts with acids to release carbon dioxide gas.

Option 2 is correct.
Baking soda (NaHCO₃) is a mild base, not acidic, so option 1 is wrong.
It reacts with acids releasing carbon dioxide gas, which is why it is used in cooking to leaven dough.
Option 3 is incorrect as it does react, especially with acids.
Option 4 is also incorrect because it is a mild base, not a strong base, and does not strongly turn red litmus to blue.
Hence, the correct statement is that baking soda reacts with acids to release CO2 gas.
Final answer: Option 2
RRB JE CBT-1 2025-26 – 19 February 2026 Shift 2 · Common salts - preparation and uses (baking soda, washing soda, bleaching powder, plaster of Paris)

Q74. Bleaching powder is commonly used:

  1. (a) As a fuel
  2. (b) To disinfect water
  3. (c) To make soap
  4. (d) As a sweetener
Answer & solution

Answer: (b) To disinfect water

Bleaching powder is widely used to disinfect water.
It helps kill bacteria and other pathogens making water safe for drinking.
This property is due to the presence of chlorine in bleaching powder.
Other options like fuel, soap making, or sweeteners are incorrect use cases for bleaching powder.
Final answer: Option 2
RRB JE CBT-1 2025-26 – 19 February 2026 Shift 2 · Common salts - preparation and uses (baking soda, washing soda, bleaching powder, plaster of Paris)

Q75. Which of the following statements about Plaster of Paris (POP) is CORRECT?

  1. (a) POP is CaSO4·½H₂O and hardens by reacting with water
  2. (b) POP is CaSO4·½H₂O and sets slowly without water
  3. (c) POP is CaSO4·2H2O and sets quickly on mixing with water
  4. (d) POP is CaSO4·2H2O and is mainly used as a fertilizer
Answer & solution

Answer: (a) POP is CaSO4·½H₂O and hardens by reacting with water

Plaster of Paris (POP) is chemically calcium sulfate hemihydrate, CaSO4·½H2O.
POP sets and hardens when mixed with water; it chemically reacts to form gypsum (CaSO4·2H2O).
Option 1 states that POP is CaSO4·½H2O and hardens by reacting with water, which is correct.
Options 2, 3, and 4 contain incorrect chemical formulas or applications.
Hence, the correct statement about POP is option 1.
Final answer: Option 1
RRB JE CBT-1 2025-26 – 19 February 2026 Shift 1 · Common salts - preparation and uses (baking soda, washing soda, bleaching powder, plaster of Paris)

Q76. Which of the following statements about washing soda is CORRECT?

  1. (a) Washing soda is chemically sodium carbonate decahydrate (Na2CO3·10H2O)
  2. (b) Washing soda is acidic in nature
  3. (c) It is obtained by heating sodium bicarbonate to 100°C
  4. (d) It does not remove permanent hardness of water
Answer & solution

Answer: (a) Washing soda is chemically sodium carbonate decahydrate (Na2CO3·10H2O)

Washing soda is sodium carbonate decahydrate with the chemical formula Na2CO3·10H2O.
It is a basic salt, so it is not acidic in nature (Option 2 is wrong).
Washing soda is obtained by heating sodium bicarbonate at about 200°C, not 100°C (Option 3 is wrong).
It is used to remove permanent hardness of water, so Option 4 is incorrect.
Therefore, the correct statement is Option 1.
Final answer: Option 1
SSC MTS 2025 – 12 February 2026 Shift 1 · Common salts - preparation and uses (baking soda, washing soda, bleaching powder, plaster of Paris)

Q77. Which of the following is the use of bleaching powder?

  1. (a) It is used in soda-acid fire extinguishers.
  2. (b) As an oxidising agent in many chemical industries.
  3. (c) It is used for removing permanent hardness of water.
  4. (d) It is used in the manufacture of sodium compounds such as borax.
Answer & solution

Answer: (b) As an oxidising agent in many chemical industries.

Correct Answer: Option 2 – As an oxidising agent in many chemical industries.
Bleaching powder (Ca( OCl )Cl) is widely used as an oxidising agent in chemical industries. Its oxidising property makes it useful for bleaching fabrics, paper pulp, and also for disinfecting water.
Why other options are wrong:
Option 1: Soda-acid fire extinguishers use sodium bicarbonate and sulphuric acid — bleaching powder is not involved.
Option 3: Permanent hardness of water is removed by washing soda (sodium carbonate), not bleaching powder.
Option 4: Borax is a sodium compound manufactured through different processes; bleaching powder is not used in its production.
SSC MTS 2025 – 11 February 2026 Shift 1 · Natural acids and their sources

Q78. Which of the following is the natural source of acetic acid?

  1. (a) Tomato
  2. (b) Orange
  3. (c) Tamarind
  4. (d) Vinegar
Answer & solution

Answer: (d) Vinegar

The correct answer is Vinegar (Option 4). Vinegar is the natural source of acetic acid (ethanoic acid), containing approximately 5–8% acetic acid. It is produced by the fermentation of ethanol by acetic acid bacteria. Option 1 (Tomato) contains citric and malic acid. Option 2 (Orange) contains citric acid. Option 3 (Tamarind) contains tartaric acid.
SSC MTS 2025 – 10 February 2026 Shift 1 · Indicators (natural, synthetic, olfactory)

Q79. Which of the following is example of synthetic indicator?
I. Methyl orange
II. Phenolphthalein

  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: 3 – Both I and II.
Synthetic indicators are artificially prepared chemical substances used to detect the acidic or basic nature of a solution by changing colour . Both Methyl orange (I) and Phenolphthalein (II) are synthetic indicators.
Methyl orange: turns red in acidic solutions and yellow in basic solutions.
Phenolphthalein: remains colourless in acidic/neutral solutions and turns pink/magenta in basic solutions.
Options 1 (Only I) and 2 (Only II) are incorrect as both are synthetic indicators. Option 4 (Neither) is incorrect.
SSC MTS 2025 – 9 February 2026 Shift 1 · Neutralisation reaction

Q80. What are the products in a reaction where an acid reacts with a base?

  1. (a) Acid and water
  2. (b) Base and water
  3. (c) Salt and water
  4. (d) Gas and water
Answer & solution

Answer: (c) Salt and water

Correct Answer: 3 (Salt and water)
When an acid reacts with a base, the reaction is called a neutralisation reaction. The products formed are salt and water.
Acid + Base → Salt + Water
Example: HCl + NaOH → NaCl + H2O (Hydrochloric acid + Sodium hydroxide → Sodium chloride + Water)
Option 1 (Acid and water) is incorrect - acid is consumed in the reaction, not produced.
Option 2 (Base and water) is incorrect - the candidate chose this wrong option; base is consumed, not produced.
Option 4 (Gas and water) is incorrect - some reactions produce gas, but the general rule for acid-base neutralisation is salt and water.
Delhi Police Head Constable (Ministerial) 2025-26 – 12 January 2026 Shift 1 · Natural acids and their sources

Q81. What makes lemon juice an effective natural cleaner?

  1. (a) High sugar content
  2. (b) Citric acid
  3. (c) Carbon dioxide
  4. (d) Potassium nitrate
Answer & solution

Answer: (b) Citric acid

Citric acid is correct. Lemon juice contains approximately 5–8% citric acid, which is responsible for its cleaning power. Citric acid is a mild acid that can dissolve mineral deposits (limescale, rust stains), break down grease, kill bacteria and mold, and act as a natural bleaching agent — making it an effective and eco-friendly cleaner.
• High sugar content: Lemons do contain a small amount of sugar, but sugar has no cleaning properties; it would actually promote bacterial growth.
• Carbon dioxide: CO₂ is a gas; lemons do not contain significant CO₂, and it has no cleaning ability in this context.
• Potassium nitrate: This is not found in lemons; it is a chemical compound used in fertilizers and explosives, unrelated to lemon's cleaning properties.
Delhi Police Head Constable (Ministerial) 2025-26 – 10 January 2026 Shift 2 · Natural acids and their sources

Q82. Which acid is responsible for the sour taste in curd?

  1. (a) Acetic acid
  2. (b) Lactic acid
  3. (c) Citric acid
  4. (d) Formic acid
Answer & solution

Answer: (b) Lactic acid

Lactic acid is correct. During the fermentation of milk into curd, bacteria (mainly Lactobacillus) convert lactose (milk sugar) into lactic acid. This lactic acid gives curd its characteristic sour taste and also causes the milk proteins to coagulate, forming the semi-solid texture.
• Acetic acid: Found in vinegar; responsible for vinegar's sourness, not curd's .
• Citric acid: Found in citrus fruits like lemons and oranges.
• Formic acid: Found in ant stings and some plants; not produced in curd.
Delhi Police Constable (Exe) 2025-26 – 4 January 2026 Shift 2 · Strong and weak acids and bases

Q83. Which of the following is a strong acid?

  1. (a) HCl (Hydrochloric acid)
  2. (b) H₂CO₃ (Carbonic acid)
  3. (c) H₂S (Hydrogen sulphide )
  4. (d) CH₃COOH (Acetic acid)
Answer & solution

Answer: (a) HCl (Hydrochloric acid)

HCl (Hydrochloric acid) is a strong acid that completely dissociates into hydrogen ions (H⁺) and chloride ions (Cl⁻) in aqueous solution.
(b) Incorrect: H₂CO₃ (Carbonic acid) is a weak acid that only partially dissociates in water.
(c) Incorrect: H₂S (Hydrogen sulphide ) is a weak acid with a very low dissociation constant.
(d) Incorrect: CH₃COOH (Acetic acid) is a weak acid that only partially dissociates, which is why vinegar (dilute acetic acid) has a mild taste.
RRB NTPC UG CBT-1 2024-25 – 9 September 2025 Shift 3 · Properties of acids

Q84. Which pair acts as a conjugate acid–base pair?

  1. (a) Cl₂ and Cl⁻
  2. (b) NaOH and OH⁻
  3. (c) H₂O and HCl
  4. (d) NH₄⁺ and NH₃
Answer & solution

Answer: (d) NH₄⁺ and NH₃

RRB NTPC UG CBT-1 2024-25 – 4 September 2025 Shift 2 · Common salts - preparation and uses (baking soda, washing soda, bleaching powder, plaster of Paris)

Q85. What is the industrial name for calcium sulphate hemihydrate?

  1. (a) Gypsum
  2. (b) Quick lime
  3. (c) Plaster of Paris
  4. (d) Slaked lime
Answer & solution

Answer: (c) Plaster of Paris

RRB NTPC UG CBT-1 2024-25 – 4 September 2025 Shift 2 · pH scale and its importance

Q86. What is the known equation that connects the concentration of a buffer solution's constituents, weak acid/salt or weak base/salt, and its pH?

  1. (a) Nernst - Boyle equation
  2. (b) Henderson-Hasselbalch equation
  3. (c) Van't Hoff equation
  4. (d) Arrhenius equation
Answer & solution

Answer: (b) Henderson-Hasselbalch equation

RRB NTPC UG CBT-1 2024-25 – 4 September 2025 Shift 3 · Common salts - preparation and uses (baking soda, washing soda, bleaching powder, plaster of Paris)

Q87. Which of the following gases is released when baking soda reacts with vinegar?

  1. (a) Carbon dioxide
  2. (b) Ammonia
  3. (c) Hydrogen
  4. (d) Carbon monoxide
Answer & solution

Answer: (a) Carbon dioxide

RRB NTPC UG CBT-1 2024-25 – 2 September 2025 Shift 1 · Properties of acids

Q88. Which of the following is the conjugate base of HCl?

  1. (a) Cl⁺
  2. (b) Cl⁻
  3. (c) H₃O⁺
  4. (d) OH⁻
Answer & solution

Answer: (b) Cl⁻

RRB NTPC UG CBT-1 2024-25 – 29 August 2025 Shift 2 · pH scale and its importance

Q89. A solution with a pH of 2 is how many times more acidic than a solution with pH 4?

  1. (a) 2 times
  2. (b) 100 times
  3. (c) 200 times
  4. (d) 10 times
Answer & solution

Answer: (b) 100 times

RRB NTPC UG CBT-1 2024-25 – 12 August 2025 Shift 2 · Common salts - preparation and uses (baking soda, washing soda, bleaching powder, plaster of Paris)

Q90. What is baking soda chemically known as?

  1. (a) Sodium carbonate
  2. (b) Sodium bicarbonate
  3. (c) Calcium carbonate
  4. (d) Magnesium hydroxide
Answer & solution

Answer: (b) Sodium bicarbonate

RRB NTPC UG CBT-1 2024-25 – 8 August 2025 Shift 2 · Properties of acids

Q91. According to the Brønsted-Lowry theory, which of the following defines an acid?

  1. (a) Donates a hydroxide ion
  2. (b) Accepts a proton
  3. (c) Donates a proton
  4. (d) Accepts an electron pair
Answer & solution

Answer: (c) Donates a proton

RRB NTPC UG CBT-1 2024-25 – 7 August 2025 Shift 3 · Properties of acids

Q92. Which of the following is NOT a characteristic of acids?

  1. (a) They turn blue litmus red.
  2. (b) They have a sour taste.
  3. (c) They release OH− ions in water.
  4. (d) They react with bases to form salt and water.
Answer & solution

Answer: (c) They release OH− ions in water.

SSC Selection Post 2025 (Phase XIII) – 2 August 2025 Shift 1 · Common salts - preparation and uses (baking soda, washing soda, bleaching powder, plaster of Paris)

Q93. What is another use of bleaching powder besides bleaching?

  1. (a) Making soap
  2. (b) Disinfecting drinking water
  3. (c) Making detergent
  4. (d) Making paint
Answer & solution

Answer: (b) Disinfecting drinking water

Correct Answer: Option 2 – Disinfecting drinking water
Bleaching powder (calcium hypochlorite / calcium oxychloride – Ca(OCl)Cl) is widely used to disinfect drinking water and swimming pools due to its strong oxidizing and germicidal properties. It kills bacteria and pathogens, making water safe for consumption.
Option 1 (Making soap): Soap is made by saponification of fats/oils with alkalis like NaOH/KOH; bleaching powder is not used.
Option 3 (Making detergent): Detergents are synthetic surfactants; bleaching powder is not a raw material.
Option 4 (Making paint): Bleaching powder is not a component in paint manufacturing.
RRB NTPC GL CBT-1 2024-25 – 19 June 2025 Shift 1 · Strong and weak acids and bases

Q94. If HF is a weak acid, what can be inferred about the strength of its conjugate base F⁻?

  1. (a) It is a weak base.
  2. (b) It is a strong base.
  3. (c) It is neutral.
  4. (d) It is a strong acid.
Answer & solution

Answer: (a) It is a weak base.

RRB NTPC GL CBT-1 2024-25 – 18 June 2025 Shift 3 · Strong and weak acids and bases

Q95. Which of the following pairs is an acid-base conjugate pair?

  1. (a) NH₄⁺ and NH₃
  2. (b) H⁺ and O²⁻
  3. (c) H₂O and H₂O₂
  4. (d) HCl and Cl₂
Answer & solution

Answer: (a) NH₄⁺ and NH₃

RRB NTPC GL CBT-1 2024-25 – 14 June 2025 Shift 1 · pH scale and its importance

Q96. A buffer solution has [CH₃COOH] = 0.1 M and [CH₃COO⁻] = 0.1 M. If pKa of CH₃COOH is 4.76, then what is its pH?

  1. (a) 4.76
  2. (b) 3.76
  3. (c) 5.76
  4. (d) 7.00
Answer & solution

Answer: (a) 4.76

RRB NTPC GL CBT-1 2024-25 – 11 June 2025 Shift 1 · Common salts - preparation and uses (baking soda, washing soda, bleaching powder, plaster of Paris)

Q97. Which of the following is NOT the use of baking soda in the kitchen?

  1. (a) As an ingredient in antacids
  2. (b) In fire extinguishers
  3. (c) As a leavening agent
  4. (d) For food colouring
Answer & solution

Answer: (d) For food colouring

RRB NTPC GL CBT-1 2024-25 – 9 June 2025 Shift 2 · Neutralisation reaction

Q98. Which of the following is a common component in toothpaste, for cleaning the teeth by neutralising the excess acid to prevent tooth decay?

  1. (a) Halogens
  2. (b) Acids
  3. (c) Bases
  4. (d) Salts
Answer & solution

Answer: (c) Bases

RRB NTPC GL CBT-1 2024-25 – 6 June 2025 Shift 2 · Properties of acids

Q99. What is the primary contributor to the sour taste in foods like lemons, vinegar and yoghurt?

  1. (a) Alkaloids
  2. (b) Bases
  3. (c) Acids
  4. (d) Salts
Answer & solution

Answer: (c) Acids

RRB NTPC GL CBT-1 2024-25 – 5 June 2025 Shift 3 · Neutralisation reaction

Q100. Which of the following foods would you advise to neutralise excess stomach acids?

  1. (a) Vinegar
  2. (b) Lemon juice
  3. (c) Baking soda
  4. (d) Spicy peppers
Answer & solution

Answer: (c) Baking soda

12

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