Answer :
Adding HCl to the Grignard reagent before benzophenone would result in the deactivation of the Grignard reagent, as it would react with HCl to produce an alkane and MgCl2, making the subsequent addition of benzophenone ineffective for the desired carbon-carbon bond formation.
If you add HCl to the Grignard reagent before adding benzophenone, you invariably deactivate the Grignard reagent. Grignard reagents are extremely nucleophilic and also very basic. They will react instantly with proton sources like HCl, resulting in the production of the corresponding alkane and magnesium chloride (MgCl2). The addition of benzophenone after this reaction would have no effect because the Grignard reagent would no longer be active to react with the benzophenone and form the desired alcohol product after hydrolysis. The initially formed Grignard reagent would be protonated and converted to its corresponding hydrocarbon (R-H), and thus, the carbon-carbon bond formation would not occur.
