See image — Hydrocarbons Chemistry Question

💡 Solution & Explanation

Concept: Heat of combustion increases with molecular size and strain energy. For isomers, more stable compounds have lower heats of combustion (they release less energy upon burning). Option (a): Methylcyclohexane > methylcyclopentane > methylcyclobutane. As ring size decreases from 6 to 5 to 4, ring strain increases, so heat of combustion increases. However, methylcyclohexane has more carbon atoms than the others... wait, all three have the same molecular formula (they are not isomers). Actually methylcyclohexane (C8H16 if we consider substituent... no: methylcyclohexane = C7H14, methylcyclopentane = C6H12, methylcyclobutane = C5H10). They are not isomers; larger molecules release more heat. So the order shown (methylcyclohexane > methylcyclopentane > methylcyclobutane) is correct based on more carbons = more heat of combustion. Option (b): The structures show bicyclic strained systems. More strained bicyclic compounds have higher heats of combustion. The order shown (more strained/larger > medium > cyclopropane-like) is consistent with increasing strain and size releasing more heat. Option (c): Iso-butene > trans-2-butene > 1-butene. For isomeric butenes (C4H8), the heat of combustion reflects stability — more stable isomers have LOWER heat of combustion. Stability order of butenes: trans-2-butene > 1-butene > isobutene (2-methylpropene) based on degree of substitution and hyperconjugation. Actually, the correct stability order is: trans-2-butene > cis-2-butene > 1-butene > isobutene. More stable = lower heat of combustion. So the heat of combustion order should be: isobutene > 1-butene > trans-2-butene (least stable releases most heat... wait: isobutene is least stable among these, trans-2-butene is most stable). Correct heat of combustion order (highest to lowest): isobutene > 1-butene > trans-2-butene. The statement given says isobutene > trans-2-butene > 1-butene, which places 1-butene last (lowest heat of combustion), implying 1-butene is most stable — this is INCORRECT. The correct order should be isobutene > 1-butene > trans-2-butene. Therefore, option (c) is the incorrect statement. Option (d): n-Hexane < n-Heptane < n-Octane. As chain length increases, heat of combustion increases. This is correct. Therefore, the correct answer is C.