Question

Out of benzene and phenol which is more easily nitrated and why

Answer 1

Nitration is easier in Phenol than Benzene.

Explanation :

Nitration is an electrophilic substitution Reaction.

The rate of reaction depends upon concentration of electron density in the aromatic rings.

The Higher the concentration of elctron density in aromatic rings ,then higher will be the rate of electrophilis reaction.
Now if we consider Phenol and Benzene, 

In Phenol , due to presence of Alcohol group [OH] ,The electron density at ortho and para position increases by R+ effect..OH group is strong ring activator.
Hence due to more electron density in Phenol than benzene , the phenol nitration is easier than Benzene.

Answer 2

The answer of your question is "phenol"
This is mainly because the nitration is the electrophilic substitution reaction that depends upon the electrons density directly. More the electrons density in the ring more will be the electrophilic reaction.
And as the electron density is more in the phenol as compared to benzene due to the presence of alcoholic group there will be more electrophilic reaction rate ultimately result in more easy nitration.
Hope this will helps.