Nitration is an example of aromatic electrophilic substitution and its rate depends upon the group already present in the benzene ring. Out of benzene and phenol, which one is more easily nitrated and why ?

Explanation

Niration of benzene and phenol is an electrophilic substitution reaction. During nitration `overset(+)(N)O_(2)` (nitronium ion) is produced as an intermediate as follows

This nitronium ion (electrophile) attacks on benzene or on phenol. Phenol is more easily nitrated than benzene as the presence of `-OH` group in phenol increases the electron density at ortho and para positions in benzene ring by +R effect.
Since, the electron density is more in phenol than in benzene, therefore, phenol is more easily nitrated than benzene.