The correct statement is :

Options

A. cyclohexadiene and cyclohexane cannot be isolated with ease during controlled hydrogenation of benzene
B. one mole each of benzene and hydrogen when reacted gives 1/3 mole of cyclohexane and 2/3 mole of unreacted hydrogen
C. hydrogenation of benzene to cyclohexane is an endothermic process
D. it is easier to hydrogenate benzene when compared to cyclohexene.

Answer

A

Explanation

Due to high resonance energy `(151 kg mol^(-1))` of benzene, it is much more stable than cyclohexadiene and cyclohexene. Therefore, during hydrogenation, cyclohexadiene and cyclohexene are reduced much more readily than benzene itself. Therefore, cyclohexadiene and cyclohexene cannot be isolated easily during controlled hydrogenation of benzene. Thus, option (a) correct.
since during hydrogenation of benzene , 3 moles of `H_2` are required to produce 1 mole of cyclohexane . Therefore, with one mole of `H_2`, 1/3 mole of cyclohexane is produced but no hydrogen is left unreacted. Thus, option (b) is wrong.
Hydrogenation is an exothermic process, therefore, option (c ) is wrong.
Due to resonance stability , benzene cannot be reduced more easily as compared to cyclohexene. Thus, option (d) is wrong.