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Carbon and its Compounds PYQs – Chemistry, SSC & Railway

167 Carbon and its Compounds (Chemistry) questions asked in recent SSC and Railway exams, newest first, with exam, date & shift, answers and solutions.

📚 167 questionsSSC 4 · Railway 163
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SSC Stenographer 2026 – 12 September 2026 Shift 2 · Ethanol and ethanoic acid

Q1. Which of the following statements regarding the mechanism and applications of vinegar is incorrect?

  1. (a) Vinegar acts as a natural preservative primarily due to the antimicrobial action of acetic acid, which lowers the pH and disrupts bacterial cell membranes.
  2. (b) The production of vinegar involves the fermentation of ethanol by Acetobacter species under aerobic conditions, resulting in the formation of acetic acid.
  3. (c) Vinegar effectively removes mineral deposits (like limescale) because acetic acid reacts with calcium carbonate to form water, carbon dioxide, and soluble acetate salts
  4. (d) The cleaning effectiveness of vinegar increases when mixed with baking soda due to the formation of a strong alkaline solution that breaks down grease and proteins.
Answer & solution

Answer: (d) The cleaning effectiveness of vinegar increases when mixed with baking soda due to the formation of a strong alkaline solution that breaks down grease and proteins.

Answer: Option 4 — The cleaning effectiveness of vinegar increases when mixed with baking soda due to the formation of a strong alkaline solution that breaks down grease and proteins.
The question asks for the incorrect statement.
Vinegar (an acid) and baking soda (a base) neutralise each other: CH₃COOH + NaHCO₃ → CH₃COONa + H₂O + CO₂.
The fizz is carbon dioxide; what remains is a near-neutral sodium acetate solution, not a strong alkali — mixing them cancels the cleaning power of both.
Options 1, 2 and 3 are all true: acetic acid preserves by lowering pH, it is made by Acetobacter under aerobic conditions, and it dissolves limescale (calcium carbonate).
Revision note — Vinegar and acetic acid
• Vinegar is a 5 to 8 per cent solution of acetic acid (ethanoic acid, CH₃COOH) in water; the name comes from the French vin aigre, sour wine.
• It is made in two fermentations: yeast turns sugar into ethanol without oxygen, then Acetobacter bacteria oxidise ethanol to acetic acid in the presence of oxygen.
• Acetic acid is a weak acid (it ionises only partly); vinegar has a pH of about 2.4 to 3.4, turns blue litmus red and reacts with carbonates to release carbon dioxide.
• With calcium carbonate: CaCO₃ + 2CH₃COOH → Ca(CH₃COO)₂ + H₂O + CO₂ — this is why it removes limescale from kettles and why it fizzes with chalk powder in the adulteration test for flour.
• As a preservative in pickles and sauces it lowers the pH so that most bacteria cannot grow; glacial acetic acid is the pure, water-free form that freezes at 16.6 °C.
• Ethanol is oxidised to ethanoic acid in the laboratory by acidified potassium dichromate or alkaline potassium permanganate.
Do not mix these up
• Acetobacter vs yeast — yeast makes alcohol (anaerobic); Acetobacter makes vinegar from that alcohol (aerobic).
• Baking soda vs washing soda — baking soda is sodium hydrogencarbonate (NaHCO₃), mildly alkaline; washing soda is sodium carbonate decahydrate (Na₂CO₃·10H₂O), strongly alkaline.
Also asked from this topic: the natural source of acetic acid (vinegar); the preservative used in pickles (a 5–8% acetic acid solution); the household test for chalk in flour (fizzing with vinegar).
SSC Stenographer 2026 – 10 September 2026 Shift 3 · Allotropes of carbon

Q2. Which of the following statements correctly describes the unique properties and potential applications of Carbon Nanotubes (CNTs) in advanced technology?

  1. (a) Carbon Nanotubes are cylindrical allotropes of carbon composed of multiple layers of graphene sheets rolled concentrically, exhibiting excellent electrical conductivity, high tensile strength, and are widely used as catalysts in traditional chemical reactions.
  2. (b) Single-walled Carbon Nanotubes (SWCNTs) possess tunable electrical properties that can be either metallic or semiconducting depending on their chirality and diameter, making them promising materials for nanoelectronics and sensor applications.
  3. (c) Carbon Nanotubes inherently have low thermal conductivity but are primarily valued for their magnetic properties in spintronic devices.
  4. (d) Carbon Nanotubes degrade rapidly under atmospheric conditions, limiting their practical use in materials science and requiring constant inert environment for handling.
Answer & solution

Answer: (b) Single-walled Carbon Nanotubes (SWCNTs) possess tunable electrical properties that can be either metallic or semiconducting depending on their chirality and diameter, making them promising materials for nanoelectronics and sensor applications.

Answer: Option 2 — Single-walled Carbon Nanotubes (SWCNTs) have tunable electrical properties, metallic or semiconducting depending on chirality and diameter
A single-walled nanotube is one graphene sheet rolled into a cylinder.
The angle at which it is rolled, its chirality (n, m), decides whether the tube behaves as a metal or as a semiconductor — which is exactly why it suits nanoelectronics.
Revision note — Carbon nanotubes
• A CNT is a rolled graphene sheet; an SWCNT has one wall, an MWCNT several concentric walls. They were characterised by Sumio Iijima in 1991.
• For an (n, m) tube the conduction is metallic when n = m (the armchair type) or when (n − m) is a multiple of 3, and semiconducting otherwise — this is the tunability the answer names.
• Tensile strength is about 100 GPa and Young's modulus about 1 TPa, making a nanotube roughly 100 times stronger than steel at about one-sixth the weight.
• Thermal conductivity along the tube is very high, about 3,000 W/m·K, well above copper — so option 3, which calls it low, is false.
• CNTs are chemically stable in ordinary air, and are used in composites, battery electrodes, field-emission displays and gas sensors.
• The allotropes of carbon to remember are diamond (tetrahedral, non-conducting), graphite (hexagonal layers, conducting), graphene, fullerene (C60, Buckminsterfullerene) and carbon nanotubes.
Do not mix these up
• Diamond vs graphite — in diamond all four valence electrons are locked into bonds, so it does not conduct; graphite leaves one delocalised electron per carbon atom and does conduct.
• Graphene vs carbon nanotube — graphene is a flat sheet one atom thick; a nanotube is that same sheet rolled into a cylinder.
Also asked from this topic: the carbon allotrope with a tetrahedral structure (diamond); why diamond does not conduct while graphite does (all its electrons are used in bonding).
RRB Group D 2025-26 – 25 August 2026 Shift 1 · Allotropes of carbon

Q3. Why does diamond not conduct electricity while graphite does?

  1. (a) All electrons in diamond are involved in bonding
  2. (b) Amorphous carbon contains delocalized electrons
  3. (c) Diamond has layers that slide and conduct
  4. (d) Fullerenes have mobile electrons in cages
Answer & solution

Answer: (a) All electrons in diamond are involved in bonding

Correct Answer:
Correct Answer: Option 1 – All electrons in diamond are involved in bonding
Explanation:
In diamond, each carbon atom formsfour strong covalent bondswith neighboring carbon atoms in a rigid 3D tetrahedral structure, using up all its valence electrons in bonding. With no free/delocalized electrons available, diamond does not conduct electricity. In graphite, each carbon forms onlythreecovalent bonds (in a planar hexagonal layered structure), leaving one electron per atomdelocalized, which is free to move and conduct electricity.
Important Facts:
• Graphite's layered structure with weak forces between layers also makes it slippery/soft, used as a lubricant.
• Diamond is the hardest natural substance due to its rigid 3D covalent network.
• Both diamond and graphite are allotropes of carbon.
RRB Group D 2025-26 – 25 August 2026 Shift 3 · Soaps and detergents

Q4. What happens to soap molecules when they are added to water?

  1. (a) Hydrocarbon tails remain in water while ionic heads project outward.
  2. (b) Soap molecules dissolve randomly without forming any arrangement.
  3. (c) Ionic heads remain in water while hydrocarbon tails project outward.
  4. (d) Both ionic heads and tails remain completely inside the water.
Answer & solution

Answer: (c) Ionic heads remain in water while hydrocarbon tails project outward.

Correct Answer:
Correct Answer: Option 3 – Ionic heads remain in water while hydrocarbon tails project outward.
Explanation:
A soap molecule has a hydrophilic (water-loving) ionic head and a hydrophobic (water-repelling) hydrocarbon tail. When added to water, the ionic head stays dissolved in the water while the hydrocarbon tail sticks out of the water surface, since it is not attracted to water molecules.
Important Facts:
• When mixed with oily dirt, soap molecules form micelles, with hydrocarbon tails pointing towards the oil/grease and ionic heads pointing outward towards water.
• This dual nature (amphiphilic structure) is what makes soap an effective cleaning agent.
RRB Group D 2025-26 – 21 August 2026 Shift 1 · Homologous series

Q5. Which characteristic is shared by all members of a homologous series?

  1. (a) They have the same molecular formula
  2. (b) They have the same molecular mass
  3. (c) They have identical physical properties
  4. (d) They have similar chemical properties
Answer & solution

Answer: (d) They have similar chemical properties

Explanation:
A homologous series is a group of compounds having the same general formula, each differing from the next by a -CH2- unit, showing a gradation in physical properties (e.g., melting/boiling points) but sharing similar chemical properties because they possess the same functional group.
Correct Answer: Option 4 – They have similar chemical properties
RRB Group D 2025-26 – 21 August 2026 Shift 1 · Chemical properties of carbon compounds (combustion, oxidation, addition, substitution)

Q6. What is the main difference between an addition and a substitution reaction in carbon compounds?

  1. (a) Addition reactions remove atoms from molecules
  2. (b) Addition reactions replace one atom with another
  3. (c) Addition reactions occur only in saturated compounds
  4. (d) Addition reactions increase the number of atoms in a molecule
Answer & solution

Answer: (d) Addition reactions increase the number of atoms in a molecule

Explanation:
In an addition reaction, an unsaturated carbon compound (containing a double or triple bond) reacts with a small molecule (such as H2, in the presence of a catalyst like Ni/Pd) that adds across the multiple bond, thereby increasing the total number of atoms in the resulting molecule. This is in contrast to a substitution reaction, where one atom/group simply replaces another without a net increase in atom count.
Correct Answer: Option 4 – Addition reactions increase the number of atoms in a molecule
RRB Group D 2025-26 – 21 August 2026 Shift 3 · Soaps and detergents

Q7. How do micelles enable soaps to function effectively in cleaning oily stains from clothes?

  1. (a) They chemically break down oily molecules into polar fragments that can evaporate easily.
  2. (b) They coat the fabric surface with a hydrophobic layer that prevents water from sticking.
  3. (c) They surround and trap non-polar substances, making them soluble in water
  4. (d) They increase the pH of water so that oils form solid precipitates that can be washed away.
Answer & solution

Answer: (c) They surround and trap non-polar substances, making them soluble in water

Correct Answer:
Correct Answer: Option 3 – They surround and trap non-polar substances, making them soluble in water
Explanation:
Soap molecules formmicellesin water: their hydrophobic (non-polar) tails point inward, trapping oil/dirt, while hydrophilic (polar) heads face outward toward water. This traps the oily dirt inside the micelle, allowing it to be washed away with water.
Important Facts:
• Soap molecules have a hydrophilic head and a hydrophobic (long hydrocarbon) tail.
• Micelle formation is a physical entrapment process, not a chemical breakdown of oil.
RRB Group D 2025-26 – 20 August 2026 Shift 1 · Chemical properties of carbon compounds (combustion, oxidation, addition, substitution)

Q8. Which of the following is NOT a characteristic of substitution reactions in alkanes ?

  1. (a) Multiple products may form
  2. (b) One atom replaces another
  3. (c) Double bond is broken
  4. (d) Occurs in presence of sunlight
Answer & solution

Answer: (c) Double bond is broken

Correct Answer:
Correct Answer: Option 3 – Double bond is broken
Explanation:
Alkanes aresaturatedhydrocarbons containing only single (C–C) bonds — they have no double bonds to break. In a substitution reaction, a hydrogen atom is replaced by another atom (e.g., a halogen) in the presence of sunlight, and multiple substitution products can form. 'Double bond is broken' describes an addition reaction of unsaturated compounds, not a substitution reaction of alkanes.
Important Facts:
• Example: CH₄ + Cl₂ →(sunlight)→ CH₃Cl + HCl (substitution).
• Addition reactions occur in unsaturated compounds (alkenes/alkynes) and involve breaking of double/triple bonds.
RRB Group D 2025-26 – 20 August 2026 Shift 2 · Ethanol and ethanoic acid

Q9. Alcohol is added to petrol mainly because it is a:

  1. (a) Stronger fuel additive
  2. (b) Denser fuel additive
  3. (c) Cleaner fuel additive
  4. (d) Heavier fuel additive
Answer & solution

Answer: (c) Cleaner fuel additive

Correct Answer:
Correct Answer: Option 3 – Cleaner fuel additive
Explanation:
Ethanol (alcohol) is blended with petrol mainly because it burns more completely and cleanly, reducing harmful vehicular emissions (like carbon monoxide) and also boosting octane rating, apart from reducing dependence on crude oil imports.
Important Facts:
• India's Ethanol Blended Petrol (EBP) programme promotes ethanol as a renewable, cleaner-burning additive.
• Alcohol is neither denser, heavier, nor inherently a 'stronger' fuel than petrol.
RRB Group D 2025-26 – 20 August 2026 Shift 3 · Chemical properties of carbon compounds (combustion, oxidation, addition, substitution)

Q10. Select the option that is true regarding the following two statements labelled Assertion (A) and Reason (R).Assertion (A): In oxidation reactions, the colour of potassium permanganate disappears initially.Reason (R): Potassium permanganate reacts with alcohols and gets reduced, causing decolourisation.

  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, and 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.

Correct Answer:
Option 3 – Both A and R are true, and R is the correct explanation of A.
Explanation:
Potassium permanganate (KMnO₄) is a strong oxidizing agent (purple/pink in colour). When it oxidizes alcohols (e.g., to aldehydes/carboxylic acids), it itself gets reduced (Mn⁷⁺ → Mn²⁺/MnO₂), and its characteristic colour disappears (decolourisation). This is exactly why R correctly explains A.
RRB Group D 2025-26 – 20 August 2026 Shift 3 · Soaps and detergents

Q11. Why does a soap solution appear cloudy?

  1. (a) Because dirt is suspended in water
  2. (b) Because soap molecules dissolve completely
  3. (c) Because soap micelles are large enough to scatter light
  4. (d) Because hydrocarbons are soluble in water
Answer & solution

Answer: (c) Because soap micelles are large enough to scatter light

Correct Answer:
Option 3 – Because soap micelles are large enough to scatter light
Explanation:
In water, soap molecules aggregate into colloidal-sized clusters called micelles. These micelles are large enough (in the colloidal size range) to scatter light (Tyndall effect), which is why a soap solution appears cloudy/turbid rather than clear.
RRB Group D 2025-26 – 19 August 2026 Shift 1 · Bonding in carbon and catenation

Q12. Carbon forms millions of stable compounds, unlike most other elements. Which combination of properties best explains this behavior?

  1. (a) High chemical reactivity and tetravalency together
  2. (b) Presence of isotopes and nuclear stability
  3. (c) Low atomic mass and small atomic size
  4. (d) Strong covalent bonding and tetravalency together
Answer & solution

Answer: (d) Strong covalent bonding and tetravalency together

Correct Answer:
Correct Answer: Option 4 – Strong covalent bonding and tetravalency together
Explanation:
Carbon has 4 valence electrons, giving ittetravalency(forms 4 covalent bonds), and its small size allows it to formstrong covalent bonds, including with itself (catenation). This combination of tetravalency and strong covalent bonding lets carbon form long chains, rings, and branched structures, resulting in millions of stable compounds.
Important Facts:
• Catenation (self-linking) is exceptionally strong in carbon due to strong C-C bonds.
• Carbon is not highly chemically reactive under normal conditions — its stability comes from strong covalent bonds, not high reactivity.
RRB Group D 2025-26 – 19 August 2026 Shift 1 · Hydrocarbons - alkanes, alkenes, alkynes

Q13. What is the general formula for alkanes with 'n' carbon atoms?

  1. (a) CₙH₂ₙ
  2. (b) CₙH₂ₙ₊₁
  3. (c) CₙH₂ₙ₋₂
  4. (d) CₙH₂ₙ₊₂
Answer & solution

Answer: (d) CₙH₂ₙ₊₂

Correct Answer:
Correct Answer: Option 4 – CₙH₂ₙ₊₂
Explanation:
Alkanes are saturated hydrocarbons with only single bonds, following the general formulaCₙH₂ₙ₊₂(e.g., methane CH₄, ethane C₂H₆, propane C₃H₈).
Important Facts:
• Alkenes (one double bond) follow CₙH₂ₙ.
• Alkynes (one triple bond) follow CₙH₂ₙ₋₂.
RRB Group D 2025-26 – 19 August 2026 Shift 2 · Ethanol and ethanoic acid

Q14. Which process converts ethanol to ethene when ethanol is heated at 443 K with excess concentrated sulphuric acid?

  1. (a) Reduction of ethanol
  2. (b) Dehydration of ethanol
  3. (c) Oxidation of ethanol
  4. (d) Hydrolysis of ethanol
Answer & solution

Answer: (b) Dehydration of ethanol

Correct Answer:
Correct Answer: Option 2 – Dehydration of ethanol
Explanation:
When ethanol is heated with excess concentrated sulphuric acid at 443 K, sulphuric acid acts as a dehydrating agent, removing a water molecule from ethanol to produce ethene: C₂H₅OH → CH₂=CH₂ + H₂O. This is calleddehydration of ethanol.
Important Facts:
• Concentrated H₂SO₄ acts as a dehydrating agent in this reaction.
• This is a standard example of an elimination reaction producing an alkene from an alcohol.
RRB Group D 2025-26 – 19 August 2026 Shift 3 · Chemical properties of carbon compounds (combustion, oxidation, addition, substitution)

Q15. Unsaturated hydrocarbons usually undergo which of the following reaction mechanisms?

  1. (a) Substitution
  2. (b) Neutralization
  3. (c) Combustion
  4. (d) Addition
Answer & solution

Answer: (d) Addition

Correct Answer:
Option 4 – Addition
Explanation:
Unsaturated hydrocarbons (alkenes and alkynes) contain double or triple carbon-carbon bonds. These bonds readily undergoaddition reactions, where atoms (such as H₂, Br₂, or X₂) add across the double/triple bond, converting it into a single bond.
Important Facts:
• Saturated hydrocarbons (alkanes) mainly undergo substitution reactions.
• The bromine water test (decolorization) is used to detect unsaturation via addition reaction.
Correct Answer: Option 4 – Addition
RRB Group D 2025-26 – 18 August 2026 Shift 1 · Ethanol and ethanoic acid

Q16. Which property of alcohol makes it suitable for use as an alternative fuel in vehicles?

  1. (a) It is heavier than petrol.
  2. (b) It has a lower boiling point than water.
  3. (c) It is a gaseous fuel.
  4. (d) It burns cleanly, producing less smoke and harmful gases.
Answer & solution

Answer: (d) It burns cleanly, producing less smoke and harmful gases.

Alcohol as an alternative fuel
Alcohol (ethanol) is considered a cleaner alternative fuel because it undergoes more complete combustion, producing less smoke and fewer harmful pollutants (like carbon monoxide and particulate matter) compared to conventional fuels.
Correct Answer: It burns cleanly, producing less smoke and harmful gases.
RRB Group D 2025-26 – 18 August 2026 Shift 3 · Isomerism

Q17. A compound has the molecular formula C4H10. Which statement best describes its structure?

  1. (a) It has a cyclic structure and a single isomer
  2. (b) It must contain a carbon-carbon double bond
  3. (c) It forms only one possible structure
  4. (d) It can exist as two different isomers with straight or branched chains
Answer & solution

Answer: (d) It can exist as two different isomers with straight or branched chains

Concept: Isomerism in Alkanes
C4H10 corresponds to butane, a saturated alkane (all single bonds, no double bonds, non-cyclic since CnH2n+2 is the acyclic saturated formula). Butane exhibits chain isomerism, existing as two distinct structures:
• n-Butane: a straight (unbranched) chain of 4 carbon atoms
• Isobutane (2-methylpropane): a branched chain structure
Since there is no carbon-carbon double bond and it is not cyclic, and it has exactly two possible structures (not just one), option 4 correctly describes it.
Correct Answer: It can exist as two different isomers with straight or branched chains
RRB Group D 2025-26 – 18 August 2026 Shift 3 · Chemical properties of carbon compounds (combustion, oxidation, addition, substitution)

Q18. The combustion of carbon allotropes, like diamond and graphite, produces:

  1. (a) only carbon dioxide and heat
  2. (b) only carbon dioxide
  3. (c) carbon dioxide, heat and light
  4. (d) only carbon dioxide and light
Answer & solution

Answer: (c) carbon dioxide, heat and light

Concept: Combustion of Carbon
Diamond and graphite are both allotropes of carbon. When carbon burns in the presence of sufficient oxygen, it undergoes complete combustion: C + O₂ → CO₂. This reaction is exothermic (releases heat) and is also accompanied by a visible flame (light), so combustion of carbon produces carbon dioxide, heat, AND light together — this is the standard textbook description of carbon combustion.
Correct Answer: carbon dioxide, heat and light
RRB Group D 2025-26 – 17 August 2026 Shift 2 · IUPAC nomenclature

Q19. The IUPAC name of the compound CH₃ – CH₂ – C(CH₃)₂ – CH₂ – CH₃ is:

  1. (a) 3-ethylpentane
  2. (b) 3,3-dimethylpentane
  3. (c) 2,2-dimethylpentane
  4. (d) 2-methylhexane
Answer & solution

Answer: (b) 3,3-dimethylpentane

IUPAC Naming
The structure CH₃–CH₂–C(CH₃)₂–CH₂–CH₃ has a central carbon (C3) bonded to two ethyl groups and two methyl groups. The longest continuous carbon chain running through both ethyl groups gives a 5-carbon (pentane) chain, with two methyl substituents both located on carbon 3. This gives the name3,3-dimethylpentane.
• Numbering from either end gives the same lowest locant (3,3), so the correct IUPAC name is 3,3-dimethylpentane, not 2,2-dimethylpentane or 2-methylhexane (no 6-carbon chain is possible here) or 3-ethylpentane (there is no ethyl branch off the main chain in the correctly chosen longest chain).
Correct Answer: 3,3-dimethylpentane
RRB Group D 2025-26 – 17 August 2026 Shift 2 · Homologous series

Q20. Which property is most affected if the length of the carbon chain in an alkane increases?

  1. (a) Flammability
  2. (b) Electrical conductivity
  3. (c) Color
  4. (d) Boiling point
Answer & solution

Answer: (d) Boiling point

Effect of Chain Length on Alkane Properties
As the length of the carbon chain in an alkane increases, the molecular size and surface area increase, strengthening the van der Waals forces between molecules. This causes a steady, significant rise inboiling pointwith increasing chain length (e.g., methane boils at -162°C while decane boils at ~174°C).
• Alkanes are non-polar and non-conductive regardless of chain length (electrical conductivity is not meaningfully affected).
• Alkanes are generally colorless across chain lengths (until very long chains become waxy solids, but 'color' is not the primary affected property).
• Flammability is present across chain lengths but is not as systematically and predictably affected as boiling point.
Correct Answer: Boiling point
RRB Group D 2025-26 – 17 August 2026 Shift 3 · Bonding in carbon and catenation

Q21. Which of the following is NOT a property typically associated with most covalent compounds of carbon?

  1. (a) They have low melting points
  2. (b) They are good conductors of electricity
  3. (c) They have low boiling points
  4. (d) Carbon forms covalent bonds with other carbon atoms
Answer & solution

Answer: (b) They are good conductors of electricity

Properties of Covalent Carbon Compounds
Covalent compounds of carbon (organic compounds) typically show:
• Low melting and boiling points (weak intermolecular forces) — this IS typical.
• Carbon's ability to form covalent bonds with other carbon atoms (catenation) — this IS typical.
• Poor electrical conductivity, since covalent compounds generally lack free ions or free electrons to carry charge — so 'good conductors of electricity' is NOT a typical property.
Correct Answer: They are good conductors of electricity
RRB Group D 2025-26 – 17 August 2026 Shift 3 · Chemical properties of carbon compounds (combustion, oxidation, addition, substitution)

Q22. What happens when hydrogen (H₂) is added to an alkene in the presence of a catalyst?

  1. (a) Alkene converts into an alkane
  2. (b) Alkene undergoes substitution
  3. (c) Alkene breaks down
  4. (d) Alkene forms an alcohol
Answer & solution

Answer: (a) Alkene converts into an alkane

Hydrogenation of Alkenes
Addition of hydrogen (H₂) to an alkene (C=C double bond) in the presence of a catalyst (like Ni/Pd) is called hydrogenation.
• The double bond is broken and hydrogen atoms are added, converting the unsaturated alkene into a saturatedalkane.
• Example: CH₂=CH₂ (ethene) + H₂ → CH₃–CH₃ (ethane).
Correct Answer: Alkene converts into an alkane
RRB Group D 2025-26 – 17 August 2026 Shift 3 · Esters and esterification

Q23. What type of reaction occurs when ethanoic acid reacts with ethanol in the presence of an acid catalyst?

  1. (a) Esterification reaction
  2. (b) Combustion reaction
  3. (c) Saponification reaction
  4. (d) Neutralization reaction
Answer & solution

Answer: (a) Esterification reaction

Reaction of Ethanoic Acid with Ethanol
Ethanoic acid (CH₃COOH) reacts with ethanol (C₂H₅OH) in the presence of a small amount of acid (like concentrated H₂SO₄) as a catalyst to form an ester and water.
• CH₃COOH + C₂H₅OH → CH₃COOC₂H₅ (ethyl ethanoate, a sweet-smelling ester) + H₂O
• This is called anesterification reaction.
Correct Answer: Esterification reaction
RRB Group D 2025-26 – 14 August 2026 Shift 1 · Homologous series

Q24. What do methane, ethane and propane represent in the study of carbon compounds?

  1. (a) Chains containing single carbon atom
  2. (b) Chains containing aromatic carbon atoms
  3. (c) Chains containing increasing carbon atoms
  4. (d) Chains containing mixed metal atoms
Answer & solution

Answer: (c) Chains containing increasing carbon atoms

Answer: Option 3 – Chains containing increasing carbon atoms.
• Methane (1C), ethane (2C), propane (3C) form ahomologous series with increasing carbon atoms.
RRB Group D 2025-26 – 14 August 2026 Shift 1 · Bonding in carbon and catenation

Q25. A chemist is designing a synthetic route for a new medicine and must select a carbon compound as the starting material. Which property of carbon allows it to form a wide variety of organic molecules suitable for this task?

  1. (a) Carbon's ability to lose electrons easily
  2. (b) Carbon's ability to attract electrons strongly
  3. (c) Carbon's ability to form double bonds with oxygen
  4. (d) Carbon's ability to form four strong covalent bonds
Answer & solution

Answer: (d) Carbon's ability to form four strong covalent bonds

Answer: Option 4 – Carbon's ability to form four strong covalent bonds.
• Carbon'stetravalency and catenation(four strong covalent bonds) let it form countless organic molecules.
RRB Group D 2025-26 – 14 August 2026 Shift 2 · IUPAC nomenclature

Q26. The IUPAC name for the compound CH₃-C(CH₃)₂-CH₂-CH₃ is:

  1. (a) 2,2-Dimethylbutane
  2. (b) 2,3-Dimethylbutane
  3. (c) 3,3-Dimethylbutane
  4. (d) 1,2-Dimethylbutane
Answer & solution

Answer: (a) 2,2-Dimethylbutane

Answer: Option 1 – 2,2-Dimethylbutane.
• CH₃–C(CH₃)₂–CH₂–CH₃ has two methyl groups on carbon 2 of a butane chain ⇒2,2-dimethylbutane.
RRB Group D 2025-26 – 14 August 2026 Shift 3 · Homologous series

Q27. Compounds that differ by a –CH₂– unit belong to which type of chemical grouping?

  1. (a) Functional group
  2. (b) Ionic compound
  3. (c) Homologous series
  4. (d) Structural isomer
Answer & solution

Answer: (c) Homologous series

Answer: Option 3 – Homologous series.
• Compounds differing by a –CH₂– unit form ahomologous series.
RRB Group D 2025-26 – 14 August 2026 Shift 3 · Bonding in carbon and catenation

Q28. Which statement explains why covalent compounds generally have low melting points?

  1. (a) Free electrons
  2. (b) Weak intermolecular forces
  3. (c) Metallic bonding
  4. (d) Strong ionic attractions
Answer & solution

Answer: (b) Weak intermolecular forces

Answer: Option 2 – Weak intermolecular forces.
• Covalent compounds haveweak intermolecular forces, giving low melting points.
RRB Group D 2025-26 – 13 August 2026 Shift 1 · Chemical properties of carbon compounds (combustion, oxidation, addition, substitution)

Q29. What is formed when carbon burns in oxygen?

  1. (a) Carbon dioxide with heat and light released
  2. (b) Hydrogen gas with heat and light released
  3. (c) Carbon monoxide with heat and light released
  4. (d) Methane gas with heat and light released
Answer & solution

Answer: (a) Carbon dioxide with heat and light released

Answer: Option 1 – Carbon dioxide with heat and light released.
• C + O₂ → CO₂, releasing heat and light (combustion).
RRB Group D 2025-26 – 13 August 2026 Shift 1 · Chemical properties of carbon compounds (combustion, oxidation, addition, substitution)

Q30. Consider the following statements and select the correct option.Statement A: Addition reactions occur when two or more reactants combine to form a single product.Statement B: Alkenes and alkynes commonly undergo addition reactions.

  1. (a) Both statements A and B are correct.
  2. (b) Statement A is correct but B is incorrect.
  3. (c) Statement A is incorrect but B is correct.
  4. (d) Both statements A and B are incorrect.
Answer & solution

Answer: (a) Both statements A and B are correct.

Answer: Option 1 – Both statements A and B are correct.
• Addition = reactants combine into one product; alkenes/alkynes (unsaturated) readily undergo addition. Both true.
RRB Group D 2025-26 – 13 August 2026 Shift 2 · Functional groups

Q31. Which functional group is found in esters?

  1. (a) –OH
  2. (b) –COO–
  3. (c) –NH₂
  4. (d) –COOH
Answer & solution

Answer: (b) –COO–

Answer: Option 2 – –COO–.
• Esters contain the–COO– (ester)functional group.
RRB Group D 2025-26 – 13 August 2026 Shift 2 · Chemical properties of carbon compounds (combustion, oxidation, addition, substitution)

Q32. Why do higher homologues of alkanes produce multiple products when they react with chlorine in a substitution reaction?

  1. (a) Alkanes are aromatic
  2. (b) Chlorine replaces hydrogen at different position
  3. (c) Chlorine is unstable in nature
  4. (d) Hydrogen atoms are absent
Answer & solution

Answer: (b) Chlorine replaces hydrogen at different position

Answer: Option 2 – Chlorine replaces hydrogen at different positions.
• In substitution, chlorine can replacehydrogen at different positions, giving several products.
RRB Group D 2025-26 – 13 August 2026 Shift 3 · Ethanol and ethanoic acid

Q33. Which of the following statements about ethanol is CORRECT?

  1. (a) Ethanol is a colorless, odourless liquid that does not evaporate easily.
  2. (b) Ethanol burns with a clear blue flame, producing carbon dioxide and water.
  3. (c) Ethanol reacts with baking soda to release hydrogen gas.
  4. (d) Ethanol does not mix with water at all.
Answer & solution

Answer: (b) Ethanol burns with a clear blue flame, producing carbon dioxide and water.

Answer: Option 2 – Ethanol burns with a clear blue flame, producing carbon dioxide and water.
• Ethanol is a volatile, sweet-smelling liquid that is miscible with water and burns with ablue flamegiving CO₂ and H₂O.
RRB Group D 2025-26 – 12 August 2026 Shift 1 · Bonding in carbon and catenation

Q34. Why do covalent compounds generally have low melting points?

  1. (a) Because their molecules are large
  2. (b) Because they are composed of metals
  3. (c) Because their bonds within molecules are weak
  4. (d) Because their intermolecular forces are weak
Answer & solution

Answer: (d) Because their intermolecular forces are weak

Answer: Option 4 – Because their intermolecular forces are weak.
• Covalent compounds haveweak intermolecular forces, so little energy is needed to melt them ⇒ low melting points.
RRB Group D 2025-26 – 12 August 2026 Shift 2 · Bonding in carbon and catenation

Q35. Which of the following substances does NOT contain carbon in its chemical composition?

  1. (a) DNA
  2. (b) Proteins
  3. (c) Water
  4. (d) Carbohydrates
Answer & solution

Answer: (c) Water

Answer: Option 3 – Water.
•Water (H₂O)has no carbon; DNA, proteins and carbohydrates are all carbon compounds.
RRB Group D 2025-26 – 12 August 2026 Shift 2 · Biomolecules - chemistry (carbohydrates, proteins, fats)

Q36. Which of the following compounds contains both an amine and a carboxyl functional group?

  1. (a) Ethanol
  2. (b) Ethanal
  3. (c) Propanone
  4. (d) Glycine
Answer & solution

Answer: (d) Glycine

Answer: Option 4 – Glycine.
•Glycineis an amino acid, containing both –NH₂ (amine) and –COOH (carboxyl) groups.
RRB Group D 2025-26 – 12 August 2026 Shift 3 · Chemical properties of carbon compounds (combustion, oxidation, addition, substitution)

Q37. A student heats ethanol with alkaline potassium permanganate. Which observation confirms that the oxidation process occurred?

  1. (a) purple color of KMnO4 fades and a sharp-smelling liquid forms
  2. (b) formation of a sweet-smelling ester
  3. (c) no change in color or smell
  4. (d) evolution of a gas with a burning smell
Answer & solution

Answer: (a) purple color of KMnO4 fades and a sharp-smelling liquid forms

Answer: Option 1 – Purple colour of KMnO₄ fades and a sharp-smelling liquid forms.
• Oxidation of ethanol to ethanoic aciddecolourises KMnO₄and gives a sharp-smelling acid.
RRB Group D 2025-26 – 12 August 2026 Shift 3 · Hydrocarbons - alkanes, alkenes, alkynes

Q38. Which of the following statements best describes a saturated carbon compound?

  1. (a) A saturated carbon compound contains at least one double bond between carbon atoms.
  2. (b) A saturated carbon compound contains a benzene ring in its structure.
  3. (c) A saturated carbon compound contains only single bonds between carbon atoms.
  4. (d) A saturated carbon compound contains at least one triple bond between carbon atoms.
Answer & solution

Answer: (c) A saturated carbon compound contains only single bonds between carbon atoms.

Answer: Option 3 – Contains only single bonds between carbon atoms.
• Asaturatedcarbon compound has onlysingle (C–C) bonds(alkanes).
RRB Group D 2025-26 – 11 August 2026 Shift 1 · Chemical properties of carbon compounds (combustion, oxidation, addition, substitution)

Q39. Which of the following hydrocarbons will undergo an addition reaction most readily?

  1. (a) Ethene
  2. (b) Methane
  3. (c) Ethane
  4. (d) Propane
Answer & solution

Answer: (a) Ethene

Answer: Option 1 – Ethene.
•Ethene(C₂H₄) is unsaturated (C=C double bond), so it readily undergoesaddition reactions. The alkanes (methane, ethane, propane) do not.
RRB Group D 2025-26 – 11 August 2026 Shift 1 · Soaps and detergents

Q40. The cloudy appearance of soap solution is due to:

  1. (a) Scattering of light by micelles
  2. (b) Reflection of light by bubbles
  3. (c) Refraction of light by ions
  4. (d) Absorption of light by oil
Answer & solution

Answer: (a) Scattering of light by micelles

Answer: Option 1 – Scattering of light by micelles.
• Soap formsmicellesthatscatter light(Tyndall effect), giving the solution a cloudy/colloidal look.
RRB Group D 2025-26 – 11 August 2026 Shift 2 · Isomerism

Q41. A teacher asks students to draw the structure of butane and isobutane. What is the main difference between these two molecules?

  1. (a) Isobutane has fewer carbon atoms than butane
  2. (b) Butane is a straight-chain, while isobutane is a branched-chain isomer
  3. (c) Butane contains an aromatic ring, isobutane does not
  4. (d) Both are cyclic hydrocarbons
Answer & solution

Answer: (b) Butane is a straight-chain, while isobutane is a branched-chain isomer

Answer: Option 2 – Butane is a straight-chain, while isobutane is a branched-chain isomer.
• Both are C₄H₁₀; butane is thestraight chainand isobutane thebranchedstructural isomer.
RRB Group D 2025-26 – 11 August 2026 Shift 3 · Bonding in carbon and catenation

Q42. Which of the following best explains why ethanol conducts electricity poorly despite being a liquid and having a polar O–H bond?

  1. (a) It decomposes in water into CO₂ and H₂O
  2. (b) It is a weak base that accepts protons
  3. (c) It is a covalent compound and does not ionize in solution
  4. (d) It dissociates completely into ions in water
Answer & solution

Answer: (c) It is a covalent compound and does not ionize in solution

Answer: Option 3 – It is a covalent compound and does not ionize in solution.
• Ethanol iscovalentand does not release ions in water, so it conducts electricity poorly.
RRB Group D 2025-26 – 11 August 2026 Shift 3 · Ethanol and ethanoic acid

Q43. When ethanol reacts with sodium metal, which gas is released as a result of the reaction?

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

Answer: (c) Hydrogen gas

Answer: Option 3 – Hydrogen gas.
• Ethanol reacts with sodium to give sodium ethoxide and releasehydrogen gas.
RRB Group D 2025-26 – 10 August 2026 Shift 1 · Chemical properties of carbon compounds (combustion, oxidation, addition, substitution)

Q44. Which of the following hydrocarbons undergo addition reactions with hydrogen?

  1. (a) Saturated hydrocarbons
  2. (b) Alicyclic hydrocarbons
  3. (c) Unsaturated hydrocarbons
  4. (d) Aromatic hydrocarbons
Answer & solution

Answer: (c) Unsaturated hydrocarbons

Answer: Option 3 — Unsaturated hydrocarbons
Unsaturated hydrocarbons(with double/triple bonds) undergo addition with hydrogen → Option 3.
RRB Group D 2025-26 – 10 August 2026 Shift 1 · Bonding in carbon and catenation

Q45. Which of the following is an organic compound?

  1. (a) NaCl
  2. (b) CaCO₃
  3. (c) CH₃Cl
  4. (d) CO₂
Answer & solution

Answer: (c) CH₃Cl

Answer: Option 3 — CH₃Cl
CH₃Cl(chloromethane) is an organic (carbon-hydrogen) compound → Option 3.
RRB Group D 2025-26 – 10 August 2026 Shift 2 · Hydrocarbons - alkanes, alkenes, alkynes

Q46. Which saturated hydrocarbon has the molecular formula as C₃H₆?

  1. (a) cyclopropane
  2. (b) propane
  3. (c) propene
  4. (d) propyne
Answer & solution

Answer: (a) cyclopropane

Answer: Option 1 – Cyclopropane.
• Asaturatedhydrocarbon (only single bonds) with formulaC₃H₆must be a ring:cyclopropane.
• Propene (C₃H₆) is unsaturated; propane is C₃H₈; propyne is C₃H₄.
RRB Group D 2025-26 – 10 August 2026 Shift 3 · Chemical properties of carbon compounds (combustion, oxidation, addition, substitution)

Q47. The commonly used catalysts for hydrogenation reactions are _________ and _________.

  1. (a) conc. sulphuric acid, nickel
  2. (b) palladium, conc. sulphuric acid
  3. (c) nickel, sodium hydroxide
  4. (d) palladium, nickel
Answer & solution

Answer: (d) palladium, nickel

Answer: Option 4 – Palladium and Nickel.
• Hydrogenation of unsaturated compounds uses metal catalysts, commonlypalladium (Pd)andnickel (Ni)(also platinum).
RRB Group D 2025-26 – 10 August 2026 Shift 3 · Bonding in carbon and catenation

Q48. Why does carbon form a large number of compounds?

  1. (a) Because carbon is highly reactive
  2. (b) Because carbon forms only single bonds
  3. (c) Because the carbon-carbon bond is very strong and stable
  4. (d) Because carbon cannot form rings
Answer & solution

Answer: (c) Because the carbon-carbon bond is very strong and stable

Answer: Option 3 – Because the carbon-carbon bond is very strong and stable.
• Carbon forms a huge number of compounds due tocatenation(strong, stable C–C bonds) and its tetravalency, allowing long chains, branches and rings.
RRB Group D 2025-26 – 9 August 2026 Shift 1 · Soaps and detergents

Q49. Why is soap less effective in hard water?

  1. (a) Soap loses polarity
  2. (b) Soap forms insoluble scum
  3. (c) Soap becomes acidic
  4. (d) Soap evaporates quickly
Answer & solution

Answer: (b) Soap forms insoluble scum

Answer: Option 2 — Soap forms insoluble scum
Hard water has Ca²⁺/Mg²⁺ ions that react with soap to form aninsoluble scum, so soap lathers poorly → Option 2.
RRB Group D 2025-26 – 9 August 2026 Shift 1 · IUPAC nomenclature

Q50. For the compound CH₃-CH₂-CHO, what is its correct IUPAC name?

  1. (a) Propanone
  2. (b) Propanal
  3. (c) Propanoic acid
  4. (d) Propanol
Answer & solution

Answer: (b) Propanal

Answer: Option 2 — Propanal
CH₃-CH₂-CHO has a –CHO (aldehyde) group with 3 carbons ⟹Propanal→ Option 2.
RRB Group D 2025-26 – 9 August 2026 Shift 2 · Chemical properties of carbon compounds (combustion, oxidation, addition, substitution)

Q51. Read the following two statements carefully and choose the correct option:Statement I: Ethanol on oxidation with alkaline potassium permanganate gives ethanoic acid.Statement II: Oxidation of ethanol involves the removal of hydrogen atoms and addition of oxygen.Which of the following is correct?

  1. (a) Both statements are correct, and Statement II explains Statement I.
  2. (b) Only statement II is correct.
  3. (c) Only statement I is correct.
  4. (d) Both statements are correct, but Statement II does not explain Statement I.
Answer & solution

Answer: (a) Both statements are correct, and Statement II explains Statement I.

Answer: Option 1 — Both correct, and II explains I
Ethanol → ethanoic acid on oxidation (I ✓); oxidation = removal of H / addition of O (II ✓, and it explains I) → Option 1.
RRB Group D 2025-26 – 9 August 2026 Shift 3 · Hydrocarbons - alkanes, alkenes, alkynes

Q52. Why are saturated hydrocarbons less reactive than unsaturated hydrocarbons?

  1. (a) They have double bonds.
  2. (b) They are aromatic.
  3. (c) They contain oxygen.
  4. (d) Their single bonds are strong.
Answer & solution

Answer: (d) Their single bonds are strong.

Answer: Option 4 — Their single bonds are strong
Saturated hydrocarbons have onlystrong single bonds, making them less reactive → Option 4.
RRB Group D 2025-26 – 9 August 2026 Shift 3 · Ethanol and ethanoic acid

Q53. What happens when ethanol is heated with excess concentrated sulphuric acid at 170°C?

  1. (a) Ethanoic acid is formed
  2. (b) Methane is formed as a gas
  3. (c) Carbon dioxide is released
  4. (d) Ethene is formed by dehydration
Answer & solution

Answer: (d) Ethene is formed by dehydration

Answer: Option 4 — Ethene is formed by dehydration
Ethanol + conc. H₂SO₄ at 170°C ⟹dehydration to ethene→ Option 4.
RRB Group D 2025-26 – 6 August 2026 Shift 1 · Chemical properties of carbon compounds (combustion, oxidation, addition, substitution)

Q54. Read the following two statements carefully and choose the correct option:Statement I: When methane reacts with chlorine in the presence of sunlight, hydrogen atoms in methane are gradually replaced by chlorine atoms.Statement II: The reaction between methane and chlorine is called an addition 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: (b) Only Statement I is correct.

Answer: Option 2 — Only Statement I is correct
Methane + chlorine (sunlight) is asubstitutionreaction — H atoms are replaced by Cl (I ✓). It is NOT an addition reaction (II ✗) → Option 2.
RRB Group D 2025-26 – 6 August 2026 Shift 1 · Soaps and detergents

Q55. How does saponification relate to soap formation?

  1. (a) Saponification makes ethanol for cleaning
  2. (b) Saponification is unrelated to soap production
  3. (c) Saponification produces only esters used in flavoring
  4. (d) Saponification produces sodium or potassium salts of long chain carboxylic acids, which are soaps
Answer & solution

Answer: (d) Saponification produces sodium or potassium salts of long chain carboxylic acids, which are soaps

Answer: Option 4 — Produces sodium/potassium salts of long-chain carboxylic acids (soaps)
Saponification of fats with alkali yieldssoap(Na/K salts of fatty acids) → Option 4.
RRB Group D 2025-26 – 6 August 2026 Shift 3 · Chemical properties of carbon compounds (combustion, oxidation, addition, substitution)

Q56. The combustion of carbon or its compounds gives off:

  1. (a) Light only
  2. (b) Heat only
  3. (c) Electricity
  4. (d) Heat and light
Answer & solution

Answer: (d) Heat and light

Answer: Option 4 — Heat and light
Combustion of carbon/its compounds releasesheat and light→ Option 4.
RRB Group D 2025-26 – 6 August 2026 Shift 3 · Bonding in carbon and catenation

Q57. The number of bonds formed in ethene is:

  1. (a) 4
  2. (b) 3
  3. (c) 6
  4. (d) 5
Answer & solution

Answer: (c) 6

Answer: Option 3 — 6
Ethene (C₂H₄): 4 C–H bonds + 1 C=C (counts as 2 bonds) =6 bonds→ Option 3.
RRB Group D 2025-26 – 5 August 2026 Shift 1 · Ethanol and ethanoic acid

Q58. Molasses, a byproduct of sugar production from sugarcane, can be used as a feedstock for the production of which of the following carbon compounds through fermentation?

  1. (a) ethanol
  2. (b) propanoic acid
  3. (c) butanone
  4. (d) propanal
Answer & solution

Answer: (a) ethanol

Answer: Option 1 — ethanol
Fermentation of molasses (sugars) by yeast producesethanol→ Option 1.
RRB Group D 2025-26 – 5 August 2026 Shift 2 · Allotropes of carbon

Q59. Which of the following statements correctly identifies a key property of diamond, an allotrope of carbon, that distinguishes it from graphite?

  1. (a) Diamond exists in a layered structure like graphite.
  2. (b) Diamond conducts electricity because of delocalised electrons.
  3. (c) Diamond is a non-conductor of electricity due to the absence of free electrons.
  4. (d) Diamond has soft layers that slide over each other.
Answer & solution

Answer: (c) Diamond is a non-conductor of electricity due to the absence of free electrons.

Answer: Option 3 — Diamond is a non-conductor due to the absence of free electrons
In diamond each carbon is bonded to 4 others (no free electrons), so itdoes not conduct electricity(unlike graphite) → Option 3.
RRB Group D 2025-26 – 5 August 2026 Shift 2 · Homologous series

Q60. Which of the following statements about a homologous series are CORRECT? All members have the same general formula. Each successive member differs by a –CH₂– group. Physical properties remain identical for all members.

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

Answer: (c) Only 1 and 2

Answer: Option 3 — Only 1 and 2
A homologous series: (1) same general formula ✓, (2) successive members differ by –CH₂– ✓, (3) physical properties are NOT identical (they vary gradually) ✗. So 1 and 2 → Option 3.
RRB Group D 2025-26 – 5 August 2026 Shift 3 · Bonding in carbon and catenation

Q61. Which of the following properties of carbon leads to the formation of a large number of compounds?

  1. (a) Non flexibility
  2. (b) Combustibility and Ductility
  3. (c) Malleability and Sonority
  4. (d) Catenation and Tetravalency
Answer & solution

Answer: (d) Catenation and Tetravalency

Answer: Option 4 — Catenation and Tetravalency
Carbon forms a huge number of compounds due tocatenation(self-linking) andtetravalency(4 bonds) → Option 4.
RRB Group D 2025-26 – 5 August 2026 Shift 3 · Chemical properties of carbon compounds (combustion, oxidation, addition, substitution)

Q62. Consider the conversion of ethanol (CH₃CH₂OH) to acetic acid (CH₃COOH) using acidified potassium dichromate:Statement I: This is an example of an oxidation reaction.Statement II: Acidified potassium dichromate is an oxidizing agent.Statement III: Acidified potassium dichromate is a reducing agent.Which of the following is correct?

  1. (a) Only I is true
  2. (b) I and III are true
  3. (c) II and III are true
  4. (d) I and II are true
Answer & solution

Answer: (d) I and II are true

Answer: Option 4 — I and II are true
Ethanol → acetic acid is anoxidation(I ✓); acidified K₂Cr₂O₇ is anoxidising agent(II ✓), not a reducing agent (III ✗) → Option 4.
RRB Group D 2025-26 – 4 August 2026 Shift 1 · Ethanol and ethanoic acid

Q63. Complete oxidation of one mole of ethanol releases how many moles of CO₂?

  1. (a) Three
  2. (b) Four
  3. (c) One
  4. (d) Two
Answer & solution

Answer: (d) Two

Answer: Option 4 — Two
C₂H₅OH + 3O₂ →2CO₂+ 3H₂O. One mole of ethanol gives2 moles of CO₂→ Option 4.
RRB Group D 2025-26 – 4 August 2026 Shift 2 · Soaps and detergents

Q64. What is the principal mechanism by which soap removes oily dirt from fabrics?

  1. (a) Soap increases viscosity and dissolves impurities directly in water
  2. (b) Soap chemically reacts with oil to convert it into soluble alcohol
  3. (c) Soap evaporates water content and separates dirt through sublimation
  4. (d) Soap molecules reduce surface tension and form micelles trapping dirt
Answer & solution

Answer: (d) Soap molecules reduce surface tension and form micelles trapping dirt

Answer: Option 4 — Soap reduces surface tension and forms micelles trapping dirt
Soap molecules formmicelles(tails trapping oil, heads in water), lifting oily dirt into water → Option 4.
RRB Group D 2025-26 – 4 August 2026 Shift 3 · Allotropes of carbon

Q65. Which of the following is the carbon allotrope having a tetrahedral structure?

  1. (a) Graphene
  2. (b) Diamond
  3. (c) Fullerene
  4. (d) Graphite
Answer & solution

Answer: (b) Diamond

Answer: Option 2 — Diamond
Diamondhas a tetrahedral (each carbon bonded to 4 others) structure → Option 2.
RRB Group D 2025-26 – 4 August 2026 Shift 3 · Ethanol and ethanoic acid

Q66. Which of the following is used as a preservative in pickles?

  1. (a) 5-8% solution of acetic anhydride in water
  2. (b) 5-8% solution of acetic acid in water
  3. (c) 5-8% solution of cinnamic in water
  4. (d) 5-8% solution of ethanol in water
Answer & solution

Answer: (b) 5-8% solution of acetic acid in water

Answer: Option 2 — 5–8% solution of acetic acid in water
Vinegar (5–8% acetic acid) is used as a pickle preservative → Option 2.
RRB Group D 2025-26 – 3 August 2026 Shift 1 · Ethanol and ethanoic acid

Q67. Which property of ethanol makes it suitable for use as a solvent in medicines?

  1. (a) It is acidic in nature
  2. (b) It is highly flammable
  3. (c) It forms esters
  4. (d) Solubility
Answer & solution

Answer: (d) Solubility

Answer: Option 4 — Solubility
Concept:Ethanol dissolves bothpolar and many non-polarsubstances (it has a polar –OH group and a non-polar –C₂H₅ part) and ismiscible with water. This wide solvent power (good solubility) makes it useful for dissolving medicines (tinctures, syrups) → Option 4.
RRB Group D 2025-26 – 3 August 2026 Shift 1 · Ethanol and ethanoic acid

Q68. Which statement correctly describes the solubility of ethanol?

  1. (a) Soluble only in acids
  2. (b) Slightly soluble in water
  3. (c) Completely miscible with water
  4. (d) Insoluble in water
Answer & solution

Answer: (c) Completely miscible with water

Answer: Option 3 — Completely miscible with water
Concept:Ethanol's –OH group forms hydrogen bonds with water, so ethanol iscompletely miscible with water in all proportions→ Option 3.
RRB Group D 2025-26 – 3 August 2026 Shift 2 · Hydrocarbons - alkanes, alkenes, alkynes

Q69. Which among the following molecular formulae of organic compounds does NOT represent a ring structure?

  1. (a) C₆H₁₀
  2. (b) C₆H₁₄
  3. (c) C₆H₆
  4. (d) C₆H₈
Answer & solution

Answer: (b) C₆H₁₄

Answer: Option 2 — C₆H₁₄
A ring (or unsaturation) reduces the number of H atoms. For anopen-chain saturatedcompound CₙH₂ₙ₊₂: C₆ → 2(6)+2 =C₆H₁₄(no ring). C₆H₆ (benzene), C₆H₁₀, C₆H₈ have rings/double bonds → Option 2 is the non-ring one.
RRB Group D 2025-26 – 3 August 2026 Shift 3 · Ethanol and ethanoic acid

Q70. Refer to the two statements given below and choose the CORRECT option.Statement A: Ethanoic acid reacts with bases to form a salt and water.Statement B: This reaction is classified as an oxidation reaction.

  1. (a) Statement A is incorrect but B is correct.
  2. (b) Both statements A and B are correct.
  3. (c) Statement A is correct but B is incorrect.
  4. (d) Both statements A and B are incorrect.
Answer & solution

Answer: (c) Statement A is correct but B is incorrect.

Answer: Option 3 — A correct, B incorrect
A: ethanoic acid + base → salt + water —correct (neutralisation).
B: this is aneutralisationreaction, NOT an oxidation reaction —incorrect.
So A correct, B incorrect → Option 3.
RRB Group D 2025-26 – 3 August 2026 Shift 3 · Ethanol and ethanoic acid

Q71. Which of the following statements is true about ethanoic acid?

  1. (a) It has a soapy feel and bitter taste
  2. (b) It does not dissolve in water
  3. (c) It is used to sweeten food due to its sugar content
  4. (d) It turns blue litmus red and reacts with carbonates to produce CO₂
Answer & solution

Answer: (d) It turns blue litmus red and reacts with carbonates to produce CO₂

Answer: Option 4 — Turns blue litmus red and reacts with carbonates to give CO₂
Ethanoic acid (acetic acid) is a weak acid: itturns blue litmus redandreacts with carbonates to release CO₂→ Option 4.
RRB NTPC UG CBT-1 2025-26 – 13 June 2026 Shift 2 · Soaps and detergents

Q72. When fats react with sodium hydroxide to produce soap and glycerol, the reaction is classified as:

  1. (a) Fermentation reaction
  2. (b) Combustion reaction
  3. (c) Precipitation reaction
  4. (d) Saponification reaction
Answer & solution

Answer: (d) Saponification reaction

Topic: Chemical Reactions - Saponification
Fats/Oils + NaOH → Soap + Glycerol
Key Facts:
1. Saponification = Base hydrolysis of esters (fats)
2. Produces soap (sodium salt of fatty acid) + glycerol
3. Commercial soap-making process uses this reaction
Other options:
Fermentation → Glucose to alcohol (yeast)
Combustion → Burning with oxygen
Precipitation → Insoluble solid formation
Answer: Option 4 → Saponification reaction
RRB Technician Grade III 2025-26 – 10 March 2026 Shift 3 · Chemical properties of carbon compounds (combustion, oxidation, addition, substitution)

Q73. Addition reactions are characteristic of which type of hydrocarbons?

  1. (a) Only alkenes
  2. (b) Only alkynes
  3. (c) Only alkanes
  4. (d) Both alkynes and alkenes
Answer & solution

Answer: (d) Both alkynes and alkenes

Addition reactions involve the addition of atoms to the carbon atoms of the hydrocarbon.
Alkenes have a double bond which can break to add atoms, allowing addition reactions.
Alkynes have a triple bond which can also undergo addition reactions similarly.
Alkanes, having only single bonds, typically do not undergo addition reactions but substitution reactions.
Therefore, addition reactions are characteristic of both alkenes and alkynes, but not alkanes.
RRB Technician Grade III 2025-26 – 10 March 2026 Shift 2 · Esters and esterification

Q74. Ethanol and ethanoic acid react in the presence of concentrated sulphuric acid to form a sweet-smelling compound. Which of the following correctly identifies the reaction type and the role of concentrated H₂SO₄?

  1. (a) It is an esterification reaction; H₂SO₄ acts as a catalyst and a dehydrating agent.
  2. (b) It is a substitution reaction; H₂SO₄ acts as a dehydrating agent to remove water molecules.
  3. (c) It is a neutralization reaction; H₂SO₄ acts as an acid to neutralize the base.
  4. (d) It is an oxidation reaction; H₂SO₄ acts as an oxidizing agent.
Answer & solution

Answer: (a) It is an esterification reaction; H₂SO₄ acts as a catalyst and a dehydrating agent.

Ethanol reacts with ethanoic acid to form an ester and water.
This reaction is known as esterification.
Concentrated sulphuric acid (H₂SO₄) acts as a catalyst to speed up the reaction.
H₂SO₄ also acts as a dehydrating agent, removing the water formed to drive the reaction forward.
The product formed is a sweet-smelling compound, characteristic of esters.
Therefore, the correct identification is esterification with H₂SO₄ as catalyst and dehydrating agent.
RRB Technician Grade III 2025-26 – 10 March 2026 Shift 2 · Bonding in carbon and catenation

Q75. Read the given statements carefully and select the correct option.
Statement-I: Most carbon compounds are poor conductors of electricity.
Statement-II: Carbon compounds have low melting and boiling points as compared to ionic compounds.

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

Answer: (d) Both the statements are true.

Both statements are correct.
Statement-I: Most carbon compounds (covalent compounds) do not conduct electricity because they lack free ions or electrons.
Statement-II: Carbon compounds generally have low melting and boiling points compared to ionic compounds due to weak intermolecular forces.
Hence, both statements are true.
RRB Technician Grade III 2025-26 – 10 March 2026 Shift 3 · Allotropes of carbon

Q76. The difference in electrical conductivity between diamond and graphite arises because:

  1. (a) Graphite has delocalized electrons; diamond does not
  2. (b) Diamond has metallic bonding, graphite does not
  3. (c) Diamond has tightly packed ions
  4. (d) Both have free electrons, but in different numbers
Answer & solution

Answer: (a) Graphite has delocalized electrons; diamond does not

Graphite conducts electricity because it has delocalised electrons free to move.
Diamond does not conduct electricity due to the absence of free electrons.
Hence, the difference in electrical conductivity is due to graphite having delocalised electrons, whereas diamond does not.
Therefore, graphite is a good conductor, and diamond is an insulator.
RRB Technician Grade III 2025-26 – 10 March 2026 Shift 1 · Chemical properties of carbon compounds (combustion, oxidation, addition, substitution)

Q77. Which condition is required for methane to undergo a substitution reaction with chlorine?

  1. (a) Heat
  2. (b) Acidic medium
  3. (c) Electric current
  4. (d) Sunlight
Answer & solution

Answer: (d) Sunlight

The substitution reaction of methane with chlorine is a photochemical reaction.
It requires energy to break the bonds in the chlorine molecule to initiate the reaction.
Sunlight provides the UV radiation needed to start the reaction.
Hence, the condition required is sunlight.
RRB Technician Grade III 2025-26 – 10 March 2026 Shift 1 · Chemical properties of carbon compounds (combustion, oxidation, addition, substitution)

Q78. Which of the following is correct for substitution reaction?

  1. (a) A reaction where two compounds combine to form one.
  2. (b) A reaction where a compound breaks down into simpler substances.
  3. (c) A reaction where atoms or groups in a molecule are replaced by another atom or group.
  4. (d) A reaction where hydrogen is added to a compound.
Answer & solution

Answer: (c) A reaction where atoms or groups in a molecule are replaced by another atom or group.

Option 3 is correct for substitution reaction.
In a substitution reaction, an atom or a group in a molecule is replaced by another atom or group.
This is different from combination, decomposition, or addition reactions.
Hence, the correct definition is given by option 3.
RRB Technician Grade III 2025-26 – 10 March 2026 Shift 3 · Isomerism

Q79. Which of the following pairs are correctly matched as structural isomers?
A) Pentane − 2-methylbutane
B) Butane − 2-methylpropane
C) Benzene − cyclohexene

  1. (a) A, B and C
  2. (b) A and C only
  3. (c) B and C only
  4. (d) A and B only
Answer & solution

Answer: (d) A and B only

Structural isomers have the same molecular formula but differ in the connectivity of atoms.
Pentane (C5H12) and 2-methylbutane (C5H12) have the same formula but different structure, so they are structural isomers.
Butane (C4H10) and 2-methylpropane (C4H10) also have the same molecular formula but different structure, hence structural isomers.
Benzene (C6H6) and cyclohexene (C6H10) have different molecular formulas, so they are not structural isomers.
Therefore, pairs A and B are structural isomers, but pair C is not.
RRB Technician Grade III 2025-26 – 9 March 2026 Shift 2 · Chemical properties of carbon compounds (combustion, oxidation, addition, substitution)

Q80. Burning of a saturated hydrocarbon will result in which type of flame?

  1. (a) Yellow flame
  2. (b) Clean flame
  3. (c) Sooty flame
  4. (d) Green flame
Answer & solution

Answer: (b) Clean flame

Correct Answer:Clean flame
Solution:
Saturated hydrocarbons (alkanes)burn withcomplete combustion.
They produce ablue, clean (non-sooty) flame.
No unburnt carbon particles are formed.
Hence, the flame isclean.
RRB Technician Grade III 2025-26 – 9 March 2026 Shift 1 · Ethanol and ethanoic acid

Q81. Ethanoic acid reacts with sodium carbonate to produce:

  1. (a) Sodium acetate, carbon dioxide, and water
  2. (b) Sodium hydroxide and CO₂
  3. (c) Sodium acetate and carbon monoxide
  4. (d) Sodium acetate, hydrogen, and water
Answer & solution

Answer: (a) Sodium acetate, carbon dioxide, and water

Ethanoic acid (CH3COOH) reacts with sodium carbonate (Na2CO3) as an acid-base reaction.
This produces sodium acetate (CH3COONa), carbon dioxide (CO2), and water (H2O).
Reaction: 2CH3COOH + Na2CO3 → 2CH3COONa + CO2 + H2O
Hence, the correct products are sodium acetate, carbon dioxide, and water.
RRB Technician Grade III 2025-26 – 9 March 2026 Shift 3 · Functional groups

Q82. The compound with molecular formula C₂H₄O can belong to which of the following functional group, and what is its IUPAC name?

  1. (a) Aldehyde, ethanal
  2. (b) Alcohol, ethanol
  3. (c) Aldehyde, ethanol
  4. (d) Ether, ethane
Answer & solution

Answer: (a) Aldehyde, ethanal

The molecular formula C2H4O corresponds to an aldehyde or a ketone with one oxygen atom.
Among the given options, aldehyde with the molecular formula C2H4O is ethanal.
Ethanol (alcohol) has the molecular formula C2H6O, not C2H4O,
Ether (ethane) does not have this formula; ethane is C2H6 and ethers have different structures.
Therefore, the correct functional group is aldehyde with the IUPAC name ethanal.
RRB Technician Grade III 2025-26 – 9 March 2026 Shift 2 · Soaps and detergents

Q83. The formation of micelles in soap solution occurs due to:

  1. (a) hydrophobic and hydrophilic interactions in water
  2. (b) hydrogen bonding with water molecules
  3. (c) dispersion forces only
  4. (d) electrostatic attraction between ions
Answer & solution

Answer: (a) hydrophobic and hydrophilic interactions in water

The formation of micelles occurs because soap molecules are amphiphilic.
They have a hydrophobic (water-repelling) tail and a hydrophilic (water-attracting) head.
In water, the hydrophobic tails aggregate inward to avoid water, and hydrophilic heads face outward towards water.
This self-assembly is driven by hydrophobic and hydrophilic interactions.
Hence, micelles form due to these interactions in water.
RRB Technician Grade III 2025-26 – 9 March 2026 Shift 2 · Bonding in carbon and catenation

Q84. The versatile nature of carbon is responsible for the formation of which of the following types of compounds?

  1. (a) Ionic compounds
  2. (b) Inorganic compounds
  3. (c) Metallic compounds
  4. (d) Organic compounds
Answer & solution

Answer: (d) Organic compounds

Correct option is 4.
Carbon's versatile nature is due to its ability to form four covalent bonds.
This allows it to form a huge variety of compounds.
These compounds with carbon atoms are called organic compounds.
Other types like ionic, metallic, or inorganic compounds are not primarily formed due to carbon's versatility.
Hence, carbon's versatility leads to the formation of organic compounds.
RRB Technician Grade III 2025-26 – 9 March 2026 Shift 1 · Bonding in carbon and catenation

Q85. Which of the following is a characteristic feature of all organic compounds?

  1. (a) They always contain oxygen
  2. (b) They always form ionic bonds
  3. (c) They always contain nitrogen
  4. (d) They always contain carbon
Answer & solution

Answer: (d) They always contain carbon

Correct option is 4.
All organic compounds contain carbon as the basic element.
Presence of carbon distinguishes organic compounds from inorganic ones.
Other elements like oxygen or nitrogen may be present but are not always present.
Organic compounds typically form covalent bonds, not ionic.
Hence, carbon presence is the defining feature of all organic compounds.
RRB Technician Grade III 2025-26 – 9 March 2026 Shift 3 · Hydrocarbons - alkanes, alkenes, alkynes

Q86. Which of the following is a ring compound with the molecular formula C₆H₁₂?

  1. (a) Butane
  2. (b) Cyclohexane
  3. (c) Benzene
  4. (d) Hexane
Answer & solution

Answer: (b) Cyclohexane

The molecular formula C6H12 indicates a cycloalkane or an alkene.
Butane (C4H10) and Hexane (C6H14) are alkanes, so they do not fit this formula.
Benzene (C6H6) is an aromatic compound, not matching C6H12.
Cyclohexane is a cycloalkane with formula C6H12, a ring compound.
Hence, the correct answer is Cyclohexane, a six-carbon ring structure with formula C6H12.
RRB Technician Grade III 2025-26 – 9 March 2026 Shift 3 · Chemical properties of carbon compounds (combustion, oxidation, addition, substitution)

Q87. Which of the following is the product formed when ethene (C₂H₄) reacts with hydrogen (H₂) in the presence of a catalyst nickel?

  1. (a) Ethyne (C2H2)
  2. (b) Ethane (C2H6)
  3. (c) Propane (C3H8)
  4. (d) Propene (C3H6)
Answer & solution

Answer: (b) Ethane (C2H6)

Ethene (C2H4) is an alkene with a double bond between two carbon atoms.
When ethene reacts with hydrogen (H2) in presence of a nickel catalyst, the double bond breaks.
Hydrogen atoms add to the carbon atoms, converting ethene into ethane (C2H6).
This process is known as hydrogenation.
Hence, the product formed is Ethane (C2H6).
RRB Technician Grade III 2025-26 – 6 March 2026 Shift 2 · Hydrocarbons - alkanes, alkenes, alkynes

Q88. If the molecular mass of an alkane is 44, then its molecular formula is:

  1. (a) C₂H₆
  2. (b) C₄H₁₀
  3. (c) C₃H₈
  4. (d) CH₄
Answer & solution

Answer: (c) C₃H₈

The general formula of alkanes is CnH2n+2.
Calculate molecular mass for each option:
C2H6: (2×12) + (6×1) = 24 + 6 = 30
C3H8: (3×12) + (8×1) = 36 + 8 = 44
C4H10: (4×12) + (10×1) = 48 + 10 = 58
CH4: (1×12) + (4×1) = 12 + 4 = 16
Only C3H8 matches molecular mass 44.
Hence, molecular formula is C3H8.
Final answer: Option 3
RRB Technician Grade III 2025-26 – 6 March 2026 Shift 1 · Homologous series

Q89. Read the following statements carefully and choose the correct option.
Statement 1: Members of a homologous series differ by a –CH₂– group.
Statement 2: Each successive member of a homologous series differs from the previous one by 12 u in molecular mass.

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

Answer: (b) Statement 1 is true but Statement 2 is false.

Statement 1 is true: In a homologous series, each member differs from the next by a CH2 group.
Statement 2 is also true: The molecular mass difference between successive members is 14 u (not 12 u), because a CH2 group equals 14 u (12 u for carbon + 2 u for hydrogen).
Hence, Statement 2 is not correct in the value given (12 u) and cannot explain Statement 1 properly.
Therefore, both statements are true but Statement 2 is not the correct explanation of Statement 1.
Final answer: Option 2
RRB Technician Grade III 2025-26 – 6 March 2026 Shift 3 · IUPAC nomenclature

Q90. Select the correct option regarding the given statements.
Statement 1: The compound CH₃–CH₂–CHO is propanone.
Statement 2: Aldehydes are named using the suffix '–al'.

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

Answer: (a) Statement 1 is false but Statement 2 is true.

Statement 1: CH3–CH2–CHO is an aldehyde called propanal, not propanone.
Propanone is another name for acetone, which has the formula CH3–CO–CH3.
Statement 2: Aldehydes are correctly named with the suffix '-al'.
Therefore, Statement 1 is false but Statement 2 is true.
Final answer: Option 1
RRB Technician Grade III 2025-26 – 6 March 2026 Shift 2 · Bonding in carbon and catenation

Q91. Which of the following is NOT a reason for carbon’s versatility?

  1. (a) Catenation
  2. (b) Ability to form single, double and triple bonds
  3. (c) Tetravalency
  4. (d) Formation of ionic bonds
Answer & solution

Answer: (d) Formation of ionic bonds

Carbon is versatile due to its catenation property, allowing it to form long chains (Option 1).
Its ability to form single, double, and triple covalent bonds adds to its versatility (Option 2).
Carbon’s tetravalency means it can form four bonds, increasing bonding possibilities (Option 3).
Formation of ionic bonds is not a major reason for carbon’s versatility as it primarily forms covalent bonds.
Hence, option 4 is NOT a reason for carbon’s versatility.
Final answer: Option 4
RRB JE CBT-1 2025-26 – 25 February 2026 Shift 3 · Soaps and detergents

Q92. In a micelle, which part faces outward toward water?

  1. (a) Hydrocarbon tail
  2. (b) Grease molecule
  3. (c) Non-polar end
  4. (d) Ionic head
Answer & solution

Answer: (d) Ionic head

In a micelle formed by surfactant molecules, the ionic or polar heads face outward.
These ionic heads interact with water, making the micelle soluble in water.
The hydrocarbon tails, which are non-polar, face inward, away from water, to avoid contact with it.
Therefore, the part facing outward in a micelle towards water is the ionic head.
Final answer: Option 4
RRB JE CBT-1 2025-26 – 20 February 2026 Shift 2 · Hydrocarbons - alkanes, alkenes, alkynes

Q93. A cyclic compound that contains only single bonds is classified as:

  1. (a) Aromatic
  2. (b) Unsaturated
  3. (c) Aliphatic
  4. (d) Saturated
Answer & solution

Answer: (d) Saturated

A cyclic compound with only single bonds means it has no double or triple bonds.
Such compounds are called saturated compounds because all carbon atoms are 'saturated' with hydrogen atoms.
Unsaturated compounds contain double or triple bonds, which is not the case here.
Aromatic compounds are cyclic but contain conjugated double bonds, not only single bonds.
Aliphatic compounds can be cyclic or acyclic but saturation refers specifically to bond types in the molecule.
Therefore, the correct classification is saturated compound.
Final answer: Option 4
RRB JE CBT-1 2025-26 – 20 February 2026 Shift 3 · Soaps and detergents

Q94. A micelle has its hydrophobic ends directed:

  1. (a) Randomly in all possible directions
  2. (b) Towards water molecules directly
  3. (c) Outside forming hydrogen bonds
  4. (d) Towards the center away from water
Answer & solution

Answer: (d) Towards the center away from water

A micelle is an aggregate of surfactant molecules in a liquid colloid.
The hydrophobic (water-fearing) ends aggregate away from water.
These hydrophobic ends point towards the centre of the micelle.
The hydrophilic (water-loving) ends face outward, interacting with water molecules.
Thus, hydrophobic ends are towards the centre, away from water.
Correct option is 4.
Final answer: Option 4
RRB JE CBT-1 2025-26 – 20 February 2026 Shift 1 · Soaps and detergents

Q95. Which change will promote micelle formation in a detergent solution?

  1. (a) Adding more water to dilute the solution
  2. (b) Increasing detergent concentration above Critical Micelle Concentration(CMC)
  3. (c) Lowering the temperature below Kraft point
  4. (d) Decreasing detergent concentration below Critical Micelle Concentration(CMC)
Answer & solution

Answer: (b) Increasing detergent concentration above Critical Micelle Concentration(CMC)

Explanation:
Micelles form only when detergent concentration exceeds the Critical Micelle Concentration (CMC).
Below CMC, detergent molecules remainseparate in solution.
When concentration becomesgreater than CMC, moleculesaggregate to form micelles.
Therefore,increasing detergent concentration above CMC promotes micelle formation.
RRB JE CBT-1 2025-26 – 20 February 2026 Shift 1 · Ethanol and ethanoic acid

Q96. Which of the following does NOT describe a property of ethanol (C₂H₅OH)?

  1. (a) It is soluble in water in all proportions.
  2. (b) It is a clear, colourless liquid with a pleasant smell.
  3. (c) It turns blue litmus paper red.
  4. (d) It reacts with sodium to release hydrogen gas.
Answer & solution

Answer: (c) It turns blue litmus paper red.

Ethanol (C₂H₅OH) is neutral or very weakly acidic, so it does NOT turn blue litmus paper red.
It is soluble in water in all proportions due to hydrogen bonding with water molecules.
Ethanol is a clear, colourless liquid with a pleasant smell.
It reacts with sodium metal releasing hydrogen gas as per the reaction: 2 C₂H₅OH + 2 Na → 2 C₂H₅ONa + H₂.
Hence, the correct choice is the statement that it turns blue litmus red, which is false for ethanol.
Final answer: Option 3
RRB JE CBT-1 2025-26 – 20 February 2026 Shift 1 · Chemical properties of carbon compounds (combustion, oxidation, addition, substitution)

Q97. Which of the following statements is TRUE for all saturated hydrocarbons?

  1. (a) They contain at least one double bond.
  2. (b) They show substitution reactions rather than addition reactions.
  3. (c) They readily undergo addition reactions.
  4. (d) They are generally very reactive due to triple bonds.
Answer & solution

Answer: (b) They show substitution reactions rather than addition reactions.

Correct option: 2
Saturated hydrocarbons are alkanes with single bonds only.
They do not have double or triple bonds, so options 1 and 4 are incorrect.
Saturated hydrocarbons undergo substitution reactions rather than addition reactions because addition requires unsaturation (double/triple bonds).
Therefore, they show substitution reactions instead of addition.
Hence, option 2 is true for all saturated hydrocarbons.
This matches the chemical behaviour of saturated hydrocarbons exactly.
RRB JE CBT-1 2025-26 – 19 February 2026 Shift 3 · Chemical properties of carbon compounds (combustion, oxidation, addition, substitution)

Q98. Compare the products of complete and incomplete combustion of methane:

  1. (a) Complete → CO + H₂O; Incomplete → CO₂ + H₂O
  2. (b) Complete → CO₂ only; Incomplete → H₂O only
  3. (c) Complete → CO₂ + H₂O; Incomplete → CO + H₂O
  4. (d) Complete → CO + H₂O; Incomplete → C + H₂O
Answer & solution

Answer: (c) Complete → CO₂ + H₂O; Incomplete → CO + H₂O

Complete combustion of methane produces carbon dioxide (CO₂) and water (H₂O).
Incomplete combustion of methane produces carbon monoxide (CO) and water (H₂O) due to insufficient oxygen.
Hence, the products are:
Complete → CO₂ + H₂O
Incomplete → CO + H₂O
Final answer: Option 3
RRB JE CBT-1 2025-26 – 19 February 2026 Shift 2 · Allotropes of carbon

Q99. In graphite, a carbon atom is attached with:

  1. (a) One other carbon atom
  2. (b) Three other carbon atoms
  3. (c) Four other carbon atoms
  4. (d) Two other carbon atoms
Answer & solution

Answer: (b) Three other carbon atoms

In graphite, each carbon atom is bonded to three other carbon atoms.
This forms layers of hexagonal rings.
These layers slide over each other, making graphite soft and a good lubricant.
Option 2 is correct as the carbon atom is attached to three other carbon atoms in graphite.
Final answer: Option 2
RRB JE CBT-1 2025-26 – 19 February 2026 Shift 1 · Chemical properties of carbon compounds (combustion, oxidation, addition, substitution)

Q100. When methane (CH₄) burns completely in the presence of sufficient oxygen, which products are formed?

  1. (a) Carbon dioxide and water
  2. (b) Carbon and hydrogen
  3. (c) Carbon monoxide and water
  4. (d) Carbon dioxide and carbon
Answer & solution

Answer: (a) Carbon dioxide and water

Methane (CH₄) burns in presence of sufficient oxygen producing carbon dioxide and water.
Complete combustion means all carbon forms CO₂ and hydrogen forms H₂O.
Reaction: CH₄ + 2O₂ → CO₂ + 2H₂O.
Hence, the products are carbon dioxide and water.
Final answer: Option 1
12

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