See image — GOC and Organic Chemistry Basics Chemistry Question

💡 Solution & Explanation

Step 1: Identify the molecular formula of compound 1. Compound 1 is CH3CH2CHO (propanal). It contains 3 carbons, 6 hydrogens, and 1 oxygen. Molecular formula: C3H6O. Step 2: Check compound 2 — CH3-C(=O)-CH3 (acetone/propanone). It contains 3 carbons, 6 hydrogens, and 1 oxygen. Molecular formula: C3H6O. Same as compound 1. Compound 2 IS an isomer (functional group isomer: ketone vs aldehyde). Step 3: Check compound 3 — CH3-CH=CH-OH (prop-1-en-1-ol, an enol). It contains 3 carbons, 6 hydrogens, and 1 oxygen. Molecular formula: C3H6O. Same as compound 1. Compound 3 IS an isomer (enol tautomer/functional isomer). Step 4: Check compound 4 — the epoxide: CH2-CH-CH3 with an oxygen bridge between C1 and C2 (1,2-epoxypropane / propylene oxide). It contains 3 carbons, 6 hydrogens, and 1 oxygen. Molecular formula: C3H6O. Same as compound 1. Compound 4 IS an isomer (cyclic ether / epoxide isomer). Step 5: Since compounds 2, 3, and 4 all share the molecular formula C3H6O with compound 1, all of them are isomers of compound 1. Why other options fail: - Option (a) says only 2 is an isomer — incorrect, as 3 and 4 also qualify. - Option (b) says only 4 is an isomer — incorrect, as 2 and 3 also qualify. - Option (c) says only 2 and 3 are isomers — incorrect, as 4 also qualifies. Therefore, the correct answer is D.