Chlorobenzene can be prepared by reacting aniline with:

Aniline can be manufactured into chlorobenzene by reacting it with nitrous acid and then heating it with cuprous chloride.

The production of diazonium salt is the initial stage.

The Sandmeyer’s reaction is the next step, which involves replacing a diazonium group with a chloro group.

The preparation is given as

Hence, the correct option is D, i.e. Nitrous acid followed by heating with cuprous chloride.