In the reaction given below
The functional group which reacts with the equivalent of PhMgBr is
Ketone
Acid halide
Alkyne
Carboxylic Acid
Acid-Base reactions are preferred by Grignard Reagent as opposed to nucleophilic attacks. It is to be noted that Grignard reagents are both strongly basic as well as strongly nucleophilic. So in cases, where the acidic H is readily available (eg. COOH), acid-base reactions are preferred.
Hence, the 1 eq. of PhMgBr will react with H+ of carboxylic acid and form Benzene.
Hence, the correct option is (4).