Which of the following derivatives of alcohols is unstable in an aqueous base?

To determine which alcohol derivative is unstable in an aqueous base, we evaluate the behavior of each functional group under basic conditions and identify the one that readily undergoes hydrolysis.

An ester $$ROCOCH_3$$ contains a reactive carbonyl group and undergoes base-catalyzed hydrolysis (saponification) in the presence of aqueous alkali. During this process, the hydroxide ion attacks the electrophilic carbonyl carbon, resulting in cleavage of the ester bond to form a carboxylate salt and an alcohol. Hence, esters are unstable in aqueous base.

A benzyl ether $$ROCH_2Ph$$ is generally resistant to hydrolysis under basic conditions because the $$C-O$$ bond is not sufficiently electrophilic for nucleophilic attack by $$OH^-$$.

A tetrahydropyranyl (THP) ether is an acetal-type protecting group. Acetals are stable in basic media and are hydrolyzed only under acidic conditions.

A tert-butyl ether $$ROC(CH_3)_3$$ is also stable in aqueous base and does not undergo hydrolysis under these conditions.

Therefore, among the given alcohol derivatives, only the ester (Option A) is unstable in an aqueous base because it readily undergoes saponification.

Hence, the correct answer is Option A.