The reactivity of compound Z with different halogens under appropriate conditions is given above. The observed pattern of electrophilic substitution can be explained by:
the steric effect of the halogen
the steric effect of the tert-butyl group
the electronic effect of the phenolic group
the electronic effect of the tert-butyl group

The observed pattern of electrophilic substitution can be explained by: monosubstitution whereas the lighter halogen (chlorine) results in trisubstitution (B) the steric effect of the tert-butyl group. The steric hindrance caused by bulky tert-butyl group results in monosubstitution form heavier iodine and trisubstitution of lighter chlorine (C) the electronic effect of the phenolic group.