Question

Aryl halides are extremely less reactive towards nucleophilic substitution

Answer 1

Aryl halides are very less reactive towards nucleophilic substitution because of "Partial double bond character".
Due to this, the halide gets more strongly bonded such that nucleophilic substitution becomes difficult.

This partial double bond character occurs only when a lone pair of the halogen is in alternate position to a double bond which gives way for conjugation to happen.