(A) This reaction is reverse of esterification. As it takes place in presence of acid and the ester molecule gets hydrolysed, the reaction is called as acidic hydrolysis of ester (hydrolysis is breaking of molecule in presence of water). Acidic hydrolysis is reversible reacton, hence does not go to completion.
(B) Diisobutylaluminium hydride (DIBAL-H) is a reducing agent, which reduces ester to aldehyde.
(C) This reaction is called Stephen aldehyde synthesis which involves preparation of aldehyde from nitrile using
SnCl2,HCl and quenching of resulting iminium salt
([R−CH=NH2]+Cl−)with
H2O.
(D) Grignard reagent
(CH3MgBr) attack electrophilic carbon in the nitrile to form imine salt, this salt then gets hydrolysed to form a ketone.
Thus, the correct match is (c) A → 2, B → 3, C → 4, D → 1.