Rate of nitration is faster when substituent activates the ring (+l-effect or +R-effect, ortho\/para directing) and rate is slower when substituent deactivates the ring ( −I-effect or −R-effect, meta directing group). - Halogen deactivates ring but orientation is ortho para directing group. - Rate of C6H6=C6D6, as no effect is observed when H is replaced by D. Hence, order is I=II>IV>III