Question

why iodine can be used for electrophilic substitution of arene ?

Answer 1

due to resonance effect,differences in hybridization of c-atom in c-x bond of arene , less polarity of c-x bond, halogens (iodine) are less reactive towards nucleophilic substitution reaction . Due to resonance the election density increases at ortho and para position of haloarenes and thus undergo electrophilic substitution reaction.

Answer 2

Iodine cannot be used for electrophilic substitution of arene because the bi-product HI, due to its reducing nature, reduces the iodo arene arene making the reaction reversible.