Question

out of benzene,nitrobenzene and toluene which undergo nitration most easily and why ?

Answer 1

As nitration reactions are examples of electrophilic reactions , and the presence of electron density of compound to form nitrates is the main factor for deciding the ease of nitration reaction:

Toluene is methyl-benzene .This methyl group added to Toluene makes it special with certain properties like :
-->Methyl group is electron donating group.
-->Hence methyl group activates the benzene ring by pushing electrons on the benzene ring.
--> On the other hand nitro group on benzene is electron withdrawing group which deactivates benzene group by withdrawing the electrons from Benzene ring.

Hence the increasing order of nitration is as follows:
m-dinitrobenzene <Benzene<Toulene.

Answer 2

The ease of nitration reaction among toluene, benzene, and nitrobenzene is as follows
Toluene>benzene>nitrobenzene
It is because the ease of nitration depends upon the presence of electron density on molecules to form nitratesand these reactions are electrophilic substitution reactions. In electrophilic substitution reactions compounds having electrons are attacked by nitronium ions NO2- ions.
Because of this toluene will undergo nitration easily then benzene and then nitrobenzene.