Aryl halides are extremely less reactive towards nucleophilie substitution. Predict and explain the order of reactivity of the following compounds towards nucleophilic substitution:

Explanation

Presence of electron-withdrawing groups (such as -`NO_(2)` at o& and p- positions with respect to halogen increases the reactivity of halogens towards nucleophilic substitution reactions due to the stability of the intermediate carbonion. More the number of such groups at o- and p- positions with respect to halogen, higher is the reactivity. Thus, the order is `III gt II gt I`