The total number of sp ^ 2 hybridised carbon atoms in the major...

Lithium aluminium hydride is a strong reducing agent. It reduces cyanide to primary amine with no loss of carbon. Primary amine can undergo nucleophilic addition reaction with acetophenone to produce imine derivative. The carbon with one pi bond are ${sp}^{2}$ hybridised carbon. All the carbon in benzene ring are ${sp}^{2}$ hybridised. Hence, totally 28 ${sp}^{2}$ carbon are present in the molecule.