In the question arrange the compounds in increasing order of rate of reaction towards nucleophilic substitution.
(a) (i) < (ii) < (iii) (b) (i) < (iii) < (ii)
(c) (iii) < (ii) < (i) (d) (ii) < (iii) < (i)
Answer: (d) (ii) < (iii) < (i)
Presence of electron releasing group at ortho or para position decreases the rate of nucleophilic substitution reaction. In compound (iii), electron releasing group is present at meta position w.r.t. chlorine, so the impact is less but in compound (ii) it is present at ortho position.
Thus, the rate of reaction towards nucleophilic substitution is least in compound (ii) and highest in compound (i) as there is no electron releasing group in this compound.