Question

Sol. Key concept: Benzylic, alkyl and aromatic C–H bonds have different dissociation energies.

H₁ is benzylic: its removal gives a radical delocalised into the aromatic ring. H₂ belongs to a terminal alkyl carbon and gives a primary alkyl radical. H₃ is directly attached to an aromatic sp² carbon; its removal gives an aryl radical.

The benzylic C–H bond is the easiest of these to break, whereas the aromatic C–H bond is the strongest. Therefore C–H₃ > C–H₂ > C–H₁, which is option (c).

Correction / clarification: The high strength of the aromatic C–H bond should not be explained merely by a −I effect. Its sp² bonding and the unfavourable aryl radical are the relevant comparison.