The ease with which a nitration reaction takes place depends upon the presence of electron density on the compound to form nitrates. Nitration reactions are examples of electrophilic substitution reactions where an electron-rich species is attacked by a nitronium ion (NO₂^-).

Now, CH₃^- group is electron donating and NO₂^- is an electron withdrawing group. Therefore, toluene will have the maximum electron density among the three compounds followed by benzene.

On the other hand, m– Dinitrobenzene will have the least electron density. Hence, it will undergo nitration with comparatively more difficulty.

Hence, the increasing order of nitration is as follows:-