JEE Main 2025 · 28 January · evening · Single correct · +4 / −1
Given below are two statements:
Statement I :
and
are isomeric compounds.
Statement II :
and
are functional group isomers.
In the light of the above statements, choose the correct answer from the options given below:
- (a) Statement I is false but Statement II is true
- (b) Both Statement I and Statement II are true
- (c) Statement I is true but Statement II is false
- (d) Both Statement I and Statement II are false
Answer and solution
Answer (b) Both Statement I and Statement II are true
Solution
Chemistry ma’am · 4 steps
Write the molecular formula of each pair first, then ask what kind of difference separates them.
- Isomer test. Two compounds are isomers when they have the same molecular formula but different structures. So count the atoms in each pair before anything else.
Compound Molecular formula Key feature Methylcyclopentane C₆H₁₂ one ring Hex-3-ene C₆H₁₂ one C=C, open chain Pentan-1-amine C₅H₁₃N primary amine, -NH₂ N-Ethylpropan-1-amine C₅H₁₃N secondary amine, -NH⁻ - Statement I. Both are C₆H₁₂. A ring and a double bond each count as one degree of unsaturation, so the cyclic alkane and the alkene are ring-chain isomers. Statement I is true.
- Statement II. Both are C₅H₁₃N. One carries a primary amino group -NH₂ and the other a secondary amino group -NH⁻, and these are treated as different functional groups. So they are functional group isomers, and Statement II is true.
- So. Both statements are true, which is option (b).
The idea to keep. Same formula first, then name the difference. A ring and a C=C cost the same hydrogens, so cycloalkanes are isomers of alkenes. Primary, secondary and tertiary amines count as functional group isomers.
Answer from the NTA final answer key. Solution by PrepWiser.