Assertion: Acetic acid does not act as an acid in benzene.
Reason: Benzene does not accept a proton.
Both assertion and reason are true and the reason is the correct explanation of assertion.
A substance acts as an acid, i.e., gives a proton only when another substance present acts as a base, i.e., accepts a proton. CH3COOH cannot act as an acid in benzene because benzene cannot accept a proton, i.e., cannot act as a base.