The correct statement is

• A

  One mole each of benzene and hydrogen when reacted gives \( 1 / 3 \) mole of cyclohexane
  and \( 2 / 3 \) mole unreacted hydrogen.
• B

  It is easier to hydrogenate benzene when compared to cyclohexene.
• Correct answer
  C

  Cyclohexadiene and cyclohexene cannot be isolated with ease during controlled
  hydrogenation of benzene.
• D

  Hydrogenation of benzene to cyclohexane is an endothermic process.

Solution

During the hydrogenation of benzene only cyclohexane can be isolated.

Benzene
Cyclohexane
Therefore, cyclohexadiene and cyclohexene cannot be isolated with ease during controlled hydrogenation of benzene.

Hence, the correct answer is option: 'C'.