Reactivity in SN 2 reactions with KCN depends on the stability and nucleophilicity of the transition state.

For benzyl halides, substituents on the benzene ring affect the reactivity of the benzylic carbon through resonance and inductive effects.

Para-nitro group (-NO 2 ) is strongly electron-withdrawing, activating the benzylic carbon toward nucleophilic substitution.

Para-amino (-NH 2 ) is electron-donating, deactivating.
Para-hydroxyl (-OH) is weakly donating.
Meta-nitro group has reduced electron-withdrawal compared to para-position.
Order of reactivity based on electronic effects: para-NO 2 > meta-NO 2 > para-OH > para-NH 2 .
This gives