Out of benzene, m-dinitrobenzene and toluene, which will undergo nitration most easily and why?

Explanation

Nitration of benzene is an electrophilic substitution reaction. If there is presence of any electron releasing group such as `-CH_3`, it activates the benzene nucleus toward electrophilic substitution. If. any electron withdrawing group, such as `- NO_2` is present on benzene ring, it will deactivate benzene ring towards electrophilic substitution reaction.
So order of ease of nitration is like
Toluene `gt` Benzene `gt` m-dinitrobenzene
So toluene will undergo reaction more easily.