Question

Why chlorobenzene is more reactive as compared to the nitrobenzene?

Answer 1

Nitro- is meta directing ,that is it is a Deactivating group. Deactivating groups (that is, deactivating compared to benzene) deactivate because they withdraw electron density from the ring and make it a poorer nucleophile.
While chlorine is ortho and para durecting group. chlorine is too an electron withdrawing group but the inductive electron-withdrawing effect dominates for halogens.
Thus chlorobenzene is more reactive than nitrobenzene.