a
The order of reactivity, is dependent on the stability of the intermediate carbocation formed by cleavage of \(\mathrm{C}-\mathrm{X}\) bond. The \(3^o\) carbocation (formed from lil) will be more stable than its \(2^o\) counter part (formed from \(IV\)) which in turn will b more stable than the arenium ion (formed from \(I\) ). Also, the aryl halide has a double bond character in the \(\mathrm{C}-\mathrm{X}\) bond which makes the cleavage more difficult. However, inspite of all the stated factors, \(II\) will be more reactive than \(I\) due to the presence of the electron withdrawing - \(\mathrm{NO}_{2}\) group. \(C-X\) bond becomes weak and undergoes nucleophilic substitution reaction.