See image — Hydrocarbons Chemistry Question

💡 Solution & Explanation

Concept: The heat of combustion of alkane isomers depends on their degree of branching. Among isomers with the same molecular formula, the more branched the isomer, the lower its heat of combustion. This is because branching increases stability (lower potential energy), meaning less energy is released upon combustion. All three compounds — neo-pentane (i), iso-pentane (ii), and n-pentane (iii) — are isomers of pentane (C5H12). Degree of branching: - n-pentane (iii): unbranched (straight chain) — least stable, highest heat of combustion - iso-pentane (ii): one branch point — intermediate stability, intermediate heat of combustion - neo-pentane (i): two branch points (most branched) — most stable, lowest heat of combustion Reasoning: Since heat of combustion decreases with increasing branching: - n-pentane (iii) > iso-pentane (ii) > neo-pentane (i) - This gives the order: (iii) > (ii) > (i) Why other options fail: - (a) (i) > (ii) > (iii): This is the reverse of the correct order — incorrectly places the most branched isomer highest. - (b) (iii) > (i) > (ii): Incorrectly places neo-pentane (most branched) above iso-pentane (less branched). - (d) (i) > (iii) > (ii): Incorrect ordering with no chemical basis. Therefore, the correct answer is C.