Reactivity of alkyl halides towards SN1 nucleophilic substitution reaction is 3∘>2∘>1∘ because in SN1 nucleophilic reaction, the first and the slow step is the formation of a carbocation.
Reactivity order (decreasing order) allylic 3∘>2∘ allylic >3∘>2∘ Hence, correct option is (d).