Explanation

(c)
In the given electrophile [image:12_image453.emf]
Group is the same. So, only X affects their activity, $i.e.,$ we have to discuss activity due to
(a) $–OCH_{3}$ (b)$- Cl$
(c) [image:12_image454.emf] (d) $–S - CH_{3}$
Since, amines are less actives, therefore, electrophile (c) will be least active.