Why is phenol more easily nitrated than Benzene?

This is due to the -OH phenol functional group, which makes nitrating the molecule easier. Benzene has a delocalised pi-system above and below the plane of the molecule. The result of this is that: it is attacked by electrophiles in an electrophilic substitution reaction. Phenol also has this, but the -OH group has an oxygen atom with 2 lone pairs. One of these lone pairs are partially donated/delocalised into Benzene's pi-system, which increases the electron density across the molecule. This makes Phenol more susceptible to attack from electrophiles than Benzene and hence is more easily nitrated!