In the question arrange the compounds in increasing order of rate of reaction towards nucleophilic substitution.
(a) (i) < (ii) < (iii) (b) (ii) < (i) < (iii) (c) (iii) < (ii) < (i) (d) (i) < (iii) < (ii)
Answer: (c). (iii) < (ii) < (i)
Presence of electron releasing group at ortho and para position w.r.t. to chlorine decreases the rate of nucleophilic substitution reaction. Compound (iii) has two electron releasing groups and compound (ii) has one electron-releasing group w.r.t. chlorine while compound (i) has no electron releasing group.
So, the rate of nucleophilic reaction is highest in compound (i) an order is (iii) < (ii) < (i).