The order of reactivity is dependent on the stability of the intermediate carbocation formed by cleavage of C—X bond. The 3° carbocation formed in III will be more stable than its 2° homologue (IV) which in turn will be more stable than arenium ion (I). Moreover, the aryl halide has a double bond character in the C—X bond which makes the cleavage more difficult. On other hand II will be more reactive than I due to presence of electron withdrawing —NO₂ group. C—X bond becomes weak and undergoes nucleophilic substitution reaction

So Correct order is I < II < IV < III.