Methyl nitrile is hydrolyzed to carboxylic acid in the presence of \(H_3O^+\) as catalyst. An intermediate compound \([A]\) is formed during this reaction.

The intermediate compound [A] is:

Methyl isocyanide Ethyl amine Ethanamide Methanamide

Ethanamide

The correct answer is option 3. Ethanamide.  The reaction will be as follows: Let us look at the mechanism of the reaction: