The collection includes hydrocarbons, alcohols, polymers, organic acids, explosive substances, fuels, and related organic chemistry topics.
280. Unsaturated hydrocarbons usually produce:
[RRB Group D — 10 Feb 2026, Shift 2]
(A) Yellow flame with black smoke
(B) Clean blue flames
(C) White flame with sparkles
(D) No flame at all
Answer: (A) Yellow flame with black smoke
Explanation: Unsaturated hydrocarbons contain carbon–carbon double or triple bonds. In ordinary air they tend to burn with a luminous, smoky flame when combustion is incomplete. Soot consists of fine carbon particles, whereas complete combustion chiefly yields carbon dioxide and water.
279. Which property of carbon allows it to form a large number of compounds by bonding with itself and other elements?
[RRB Group D — 10 Feb 2026, Shift 2]
(A) Catenation
(B) Tetravalency
(C) Combustion
(D) Isomerism
Answer: (A) Catenation
Explanation: Catenation is the capacity of carbon atoms to link to other carbon atoms through stable covalent bonds. Together with tetravalency, it enables long chains, branches and rings. This structural variety explains the enormous number of organic compounds.
278. Baking soda releases which gas on heating?
[RRB Group D — 09 Feb 2026, Shift 2]
(A) CO₂
(B) H₂
(C) N₂
(D) O₂
Answer: (A) CO₂
Explanation: Sodium hydrogen carbonate decomposes on heating into sodium carbonate, water vapour and carbon dioxide. The released gas contributes to the rising of baked products. Although baking soda is an inorganic salt, its reactions are relevant to organic food acids.
277. Which of the following is a straight-chain saturated hydrocarbon?
[RRB Group D — 06 Feb 2026, Shift 1]
(A) Butane
(B) Cyclohexane
(C) Propene
(D) Benzene
Answer: (A) Butane
Explanation: Butane has four carbon atoms joined in an unbranched chain by single covalent bonds. Cyclohexane is cyclic, propene contains a double bond, and benzene is aromatic. Straight-chain alkanes have the general molecular formula CnH2n+2.
276. A molecule of methane contains one carbon atom bonded to four hydrogen atoms. What is the chemical formula for methane?
[RRB Group D — 06 Feb 2026, Shift 1]
(A) C₄H
(B) CH₄
(C) CH₃
(D) C₂H₄
Answer: (B) CH₄
Explanation: Methane is the simplest alkane. Its one carbon atom shares electrons with four hydrogen atoms, forming four single covalent bonds. The formula CH₄ also reflects the tetravalency of carbon and methane’s importance as the principal constituent of natural gas.
275. Statement A: Carboxylic acids are strong acids that completely ionise in water.
Statement B: Ethanoic acid is a weak acid compared to hydrochloric acid.
Select the correct option.
[RRB Group D — 05 Feb 2026, Shift 3]
(A) Both A and B are correct
(B) A is incorrect but B is correct
(C) Both A and B are incorrect
(D) A is correct but B is incorrect
Answer: (B) A is incorrect but B is correct
Explanation: Ethanoic acid is a weak organic acid because only a small fraction ionises in aqueous solution. Hydrochloric acid is much more extensively ionised at comparable concentrations. Therefore, the assertion about all carboxylic acids being strong is false.
274. Which of the following is a ring-chain hydrocarbon?
[RRB Group D — 05 Feb 2026, Shift 2]
(A) Propane
(B) Benzene
(C) Ethene
(D) Heptyne
Answer: (B) Benzene
Explanation: Benzene contains six carbon atoms joined in a cyclic aromatic structure. Propane, ethene and heptyne have open-chain arrangements. Benzene’s delocalised pi electrons distinguish its reactions from those of ordinary alkenes, even though both contain unsaturation.
273. What are the primary products formed during the complete combustion of most carbon compounds?
[RRB Group D — 05 Feb 2026, Shift 1]
(A) Carbon monoxide and water
(B) Carbon dioxide, water, and energy
(C) Alcohols and carboxylic acids
(D) Soot and carbon dioxide
Answer: (B) Carbon dioxide, water, and energy
Explanation: When sufficient oxygen is supplied, carbon in a combustible organic compound is oxidised mainly to carbon dioxide and hydrogen to water. Combustion also releases energy, commonly as heat and light. Oxygen deficiency may instead produce soot or carbon monoxide.
272. Which of the following is an example of a cyclic hydrocarbon?
[RRB Group D — 05 Feb 2026, Shift 1]
(A) Methane
(B) Butane
(C) Cyclohexane
(D) Ethene
Answer: (C) Cyclohexane
Explanation: Cyclohexane is a saturated ring containing six carbon atoms and has the formula C₆H₁₂. Methane has one carbon atom, butane is an open-chain alkane, and ethene is an open-chain alkene with a carbon–carbon double bond.
271. Which of the following is true about the homologous series?
[RRB Group D — 05 Feb 2026, Shift 1]
(A) Each successive member differs by a –CH₂– group
(B) All members have different functional groups
(C) All members have the same molecular weight
(D) All members have the same boiling point
Answer: (A) Each successive member differs by a –CH₂– group
Explanation: Consecutive members of a homologous series differ by one methylene unit, CH₂, equivalent to 14 atomic mass units. They share a functional group and therefore show related chemical properties, while physical properties generally vary gradually with molecular size.