Give reasons for the following
(a) The presence of `-NO_2` group at ortho or para position increases the reactivity of haloarenes towards nucleophilic substitution reactions .
(b) p-dichlorobenzene has higher melting point than of ortho or meta isomer .
( c) Thionyl chloride method is preferred for preparing alkyl chloride from alcohols.

Explanation

The presence of `-NO_2` group at ortho or para position increases the rectivity of haloarenes towards nucleophilic substitution reactions because nitro groups at ortho or para position withdraw the electron density from the benzene ring facilitating the attack of the nucleophile.
( b) Melting point of para isomer is quite higher than that of orhto or meta isomers.This is due to the fact that it has a summetrical structure and therefore ,its molecules can easily pack closely in the atmosphere leaving behind pure alkyl chlorides ,