In the given reaction

'A' can be

Explanation: The final product is triphenylmethanol $$\mathrm{Ph_3C-OH}$$.

In the reaction of an ester with a Grignard reagent, the ester provides the carbonyl carbon and one substituent attached to it.

Methyl benzoate $$\mathrm{Ph-CO-OCH_3}$$ already contains one phenyl group.

Therefore, the remaining two phenyl groups must come from the Grignard reagent.

Hence, the Grignard reagent formed in step (i) must be phenylmagnesium bromide $$\mathrm{Ph-MgBr}$$.

The reactant required to form this Grignard reagent is bromobenzene $$\mathrm{Ph-Br}$$.

The first equivalent of $$\mathrm{Ph-MgBr}$$ converts the ester into benzophenone $$\mathrm{Ph-CO-Ph}$$.

The second equivalent attacks benzophenone to form the alkoxide $$\mathrm{Ph_3C-O^-}$$.

Acidic hydrolysis then gives triphenylmethanol $$\mathrm{Ph_3C-OH}$$.

Therefore, reactant $$\mathrm{A}$$ is bromobenzene $$\mathrm{Ph-Br}$$.