Question

why does presence of nitro group make the benzene ring less reactive in comparison to the and substituted benzene ring. explain​

Answer 1

• The nitro group $-NO_2$ is an electron withdrawing group, which pulls the electron density towards itself by resonance and inductive effects.
• When in conjugation with the benzene ring, the electron density on the ring is lowered because of the nitro group.
• Since electron density is lesser than benzene, electrophilic attacks are not favoured by electrophile.
• Thus, the presence of nitro group makes it less reactive and resistant to electrophilic attacks.

Note that Nucleophilic attacks on benzene ring would be favoured in this case.