Question

Sol. [Key Concept: Rate of SN1 ionisation]

Option (2) is a secondary benzylic bromide. Loss of Br⁻ produces a carbocation stabilised by resonance with the phenyl ring and by alkyl donation, so it undergoes SN1 most readily among these choices. Bromobenzene would require a highly unstable phenyl cation; the cyclohexyl and cyclohexylmethyl substrates lack benzylic resonance stabilisation. Hence, option (2).

Hence is most reactive