See image — Isomerism and Stereochemistry Chemistry Question

💡 Solution & Explanation

Step 1: Analyze pair (a). The two structures are: (i) phenyl ester where benzoic acid esterifies para-cresol: C6H5-C(=O)-O-C6H4-CH3(para), and (ii) para-toluic acid esterifying phenol: CH3-C6H4-C(=O)-O-C6H5. Both have the same molecular formula and both are esters, but the alkyl/aryl groups on either side of the ester linkage (-C(=O)-O-) are swapped. This is the definition of metamers (same functional group, same molecular formula, but different alkyl groups on either side of the functional group). Therefore (a) matches (s) Metamers. Step 2: Analyze pair (b). The two structures are: (i) CH3-CH2-CH2-COOH (butanoic acid, straight chain, 4 carbons) and (ii) (CH3)2CH-COOH (2-methylpropanoic acid / isobutyric acid, branched chain, 4 carbons). Both are carboxylic acids with molecular formula C4H8O2, but one is straight chain and the other is branched. This is chain isomerism. Therefore (b) matches (p) Chain. Step 3: Analyze pair (c). The two structures shown are nitroalkanes: one has NO2 on C3 of pentane (3-nitropen tane) and the other has NO2 on C2 of pentane (2-nitropentane). Both have the same molecular formula C5H11NO2 and the same functional group (nitro group), but the nitro group is at different positions on the same carbon chain. This is positional isomerism. Therefore (c) matches (q) Positional. Step 4: Analyze pair (d). The two structures are based on the tetralin (1,2,3,4-tetrahydronaphthalene) framework: one has an -OH group directly on the ring (phenol-type or secondary alcohol) with a CH3 substituent, and the other has a -CH2OH group (primary alcohol/benzyl alcohol type) on the ring. Both have the same molecular formula but different functional groups: one is an aryl/secondary alcohol (-OH on ring carbon) and the other is a primary benzyl alcohol (-CH2OH). Different functional groups with the same molecular formula = functional group isomerism. Therefore (d) matches (r) Functional. Summary: (a) → (s) Metamers: same ester functional group, alkyl/aryl groups swapped around the ester linkage. (b) → (p) Chain: same carboxylic acid functional group, differ in carbon skeleton (straight vs branched). (c) → (q) Positional: same nitro functional group on same pentane chain, differ in position of NO2. (d) → (r) Functional: one is a ring-OH alcohol, other is a -CH2OH alcohol — different functional group environments / classified as functional isomers. Therefore, the correct answer is a-s; b-p; c-q; d-r.