I suppose you should authorise him to do so.

Answer: Option D

Authorise : give official permission for or approval to (an undertaking or agent).
Pulverize : reduce to fine particles.
Prescribe : (of a medical practitioner) advise and authorize the use of (a medicine or treatment) for someone, especially in writing.
Detach : disengage (something or part of something) and remove it.
Proscribe : forbid, especially by law.

Antonym of Authorise is Proscribe