Out of (ref. image), which one is more reactive towards nucleophilic substitution reaction and why?

More reactive towards nucleophilic substitution reaction. So, nucleophilic substitution means nucleophiles are attacking and benzene acts as an electrophile. As we know, the more electron-withdrawing groups present on benzene, the more electrophilic the benzene ring becomes. In B, we have a NO2 group attached to the ring. NO2 is a strong electron-withdrawing group, so it makes benzene more electrophilic as it pulls electron density towards itself. Therefore, B is more reactive towards nucleophilic substitution.