270. What is typically involved in an addition reaction?
[RRB Group D — 04 Feb 2026, Shift 3]
(A) Functional groups are replaced by others
(B) Removal of atoms from molecules takes place
(C) Atoms get added to unsaturated bonds
(D) Oxidation changes without new bonding
Answer: (C) Atoms get added to unsaturated bonds
Explanation: Addition reactions characteristically occur across carbon–carbon double or triple bonds. During the reaction, the multiple bond’s pi component is broken while new sigma bonds form with incoming atoms or groups. Hydrogenation of alkenes is a familiar example.
269. Ethanoic acid reacts with ethanol in the presence of concentrated H₂SO₄ to form:
[RRB Group D — 04 Feb 2026, Shift 1]
(A) Ethyl ethanoate
(B) Methanol
(C) Acetone
(D) Sodium acetate
Answer: (A) Ethyl ethanoate
Explanation: Ethanoic acid reacts with ethanol through esterification to produce ethyl ethanoate and water. Concentrated sulphuric acid catalyses the reaction. Ethyl ethanoate is an ester with a characteristic fruity smell, and the process is reversible.
268. What is formed when ethanol is oxidised using an oxidising agent like alkaline KMnO₄?
[RRB Group D — 04 Feb 2026, Shift 1]
(A) Methane
(B) Methanoic acid
(C) Acetone
(D) Ethanoic acid
Answer: (D) Ethanoic acid
Explanation: Ethanol is a primary alcohol that can be oxidised first to ethanal and subsequently to ethanoic acid. Strong oxidising agents such as potassium permanganate commonly drive the conversion towards the carboxylic acid. Its carbon chain remains two atoms long.
267. Which of the following is a homologous series?
[RRB Group D — 03 Feb 2026, Shift 3]
(A) Methane, methanol, methanoic acid
(B) Ethene, ethyne, ethane
(C) Methane, ethane, propane
(D) Methane, ethane, ethene
Answer: (C) Methane, ethane, propane
Explanation: Methane, ethane and propane are successive members of the alkane family. Each next member adds a CH₂ group and all follow the general formula CnH2n+2. The other sets mix compounds from different functional or bond classes.
266. Carbon has the unique ability to form bonds with other carbon atoms, giving rise to large molecules. This property is called:
[RRB Group D — 03 Feb 2026, Shift 3]
(A) Addition
(B) Catenation
(C) Unification
(D) Conjugation
Answer: (B) Catenation
Explanation: Catenation refers to self-linking among atoms of the same element. Carbon is particularly effective because its small atomic size permits strong carbon–carbon bonds. This allows the formation of stable chains and rings that underlie organic chemistry.
265. What is the primary characteristic that defines organic compounds?
[RRB Group D — 03 Feb 2026, Shift 1]
(A) They always contain oxygen
(B) They are formed only by living organisms
(C) They conduct electricity in the molten state
(D) They principally consist of carbon-based covalent structures
Answer: (D) They principally consist of carbon-based covalent structures
Explanation: Organic chemistry mainly investigates carbon compounds, particularly those with carbon–hydrogen bonds and covalent molecular frameworks. Organic compounds may also contain oxygen, nitrogen, sulphur or halogens. They need not originate in living organisms; many are synthesised industrially.
264. The reaction of an alcohol with ethanoic acid in the presence of a catalyst forms water and:
[RRB Group D — 02 Feb 2026, Shift 2]
(A) An aldehyde
(B) A hydrocarbon
(C) A salt
(D) An ester
Answer: (D) An ester
Explanation: This is esterification, a condensation process in which an alcohol and a carboxylic acid yield an ester plus water. For ethanol and ethanoic acid, the product is ethyl ethanoate. An acid catalyst increases the reaction rate.
263. Statement A: Alcohols react with sodium to evolve hydrogen.
Statement B: No gas is evolved when sodium reacts with ethanol.
Choose the correct statement.
[RRB Group D — 02 Feb 2026, Shift 2]
(A) Both A and B are correct
(B) A is correct but B is incorrect
(C) Both A and B are incorrect
(D) A is incorrect but B is correct
Answer: (B) A is correct but B is incorrect
Explanation: Reactive sodium metal displaces the hydrogen of ethanol’s hydroxyl group, yielding sodium ethoxide and hydrogen gas. Hence the first statement is true and the second false. The result distinguishes alcohol chemistry from some reactions involving hydrocarbons.
262. Which alcohol is commonly used as fuel?
[RRB Group D — 09 Jan 2026, Shift 1]
(A) Butanol
(B) Ethanol
(C) Methanol
(D) Propanol
Answer: (B) Ethanol
Explanation: Ethanol is widely used as a renewable fuel and petrol-blending component. It can be produced through fermentation of sugars from biomass. Because it contains oxygen and burns readily, its addition to petrol can influence combustion characteristics and fossil-fuel use.
261. Select the example of a functional group that does not contain a double bond in its structure.
[RRB Group D — 09 Jan 2026, Shift 1]
(A) Propanone
(B) Propanol
(C) Propanal
(D) Propanoic acid
Answer: (B) Propanol
Explanation: Propanol is an alcohol containing a hydroxyl group with single carbon–oxygen bonding. Propanone, propanal and propanoic acid each possess a carbonyl C=O group. Therefore, among the choices, propanol lacks the double bond present in the other functional groups.
