See image — Hydrocarbons Chemistry Question

💡 Solution & Explanation

Step 1: Identify the molecular formula of hexane isomers. Hexane has the molecular formula C6H14. All structural isomers of hexane share this formula. Step 2: List the four isomers already shown in the question: 1. CH3CH2CH2CH2CH2CH3 — this is n-hexane (straight chain, 6 carbons) 2. (CH3)2CHCH2CH2CH3 — this is 2-methylpentane (methyl branch on C2 of a 5-carbon chain) 3. (CH3)3CCH2CH3 — this is 2,2-dimethylbutane (two methyl groups on C2 of a 4-carbon chain) 4. (CH3)2CHCH(CH3)2 — this is 2,3-dimethylbutane (methyl groups on C2 and C3 of a 4-carbon chain) Step 3: Hexane (C6H14) has exactly five structural isomers. The five are: n-hexane, 2-methylpentane, 3-methylpentane, 2,2-dimethylbutane, and 2,3-dimethylbutane. Four of these are shown; the missing one must be 3-methylpentane. Step 4: Verify 3-methylpentane. Its structure is CH3CH2CH(CH3)CH2CH3 — a 5-carbon chain with a methyl group on C3. This is a valid C6H14 isomer not shown among the four given structures. Step 5: Evaluate the options: (a) 2-Methylpentane — already shown as (CH3)2CHCH2CH2CH3, so this is not the missing isomer. (b) 2-Ethyl butane — this name is incorrect IUPAC nomenclature; an ethyl group on C2 of butane gives the same connectivity as 3-methylpentane, but '2-ethylbutane' is not a valid or accepted IUPAC name. (c) 2,3-Dimethyl butane — already shown as (CH3)2CHCH(CH3)2, so this is not the missing isomer. (d) 3-Methyl pentane — this is the correct IUPAC name for the fifth and missing isomer of hexane. Therefore, the correct answer is D.