Based on the AIPMT 2012 context and the options provided, the reaction refers to the preparation of benzaldehyde ($C_6H_5CHO$). A common name reaction appearing in this exam yielding benzaldehyde is the Rosenmund Reduction, where benzoyl chloride ($C_6H_5COCl$) is hydrogenated over a catalyst of palladium on barium sulphate ($Pd/BaSO_4$) poisoned with sulphur or quinoline.

$C_6H_5COCl + H_2 \xrightarrow{Pd/BaSO_4} C_6H_5CHO + HCl$

Other possibilities include the Etard Reaction (oxidation of toluene with chromyl chloride) or Gattermann-Koch reaction (benzene with CO/HCl), both of which also yield benzaldehyde [1]. The product 'A' is Benzaldehyde.