The reaction involves a Grignard reagent (RMgBr) reacting with CO₂, a key reaction to form carboxylic acids. The Grignard reagent acts as a nucleophile attacking the electrophilic carbon of CO₂. After addition, aqueous workup protonates the intermediate to give the carboxylic acid.

The general reaction is: $R-\mathrm{MgBr}+\mathrm{CO}{}_2\stackrel{1.H_{2}O,H^{+}}{\to }R-\mathrm{COOH}$

In this case, the Grignard reagent is $C_6{H}_5-\mathrm{CH}-\mathrm{MgBr}$, so the product 'A' is the corresponding carboxylic acid, phenylacetic acid.

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