Average bond enthalpy of water is $464.5 \text{ kJ mol}^{-1}$. If the energy required to break the first $O-H$ bond is $502 \text{ kJ mol}^{-1}$,how much energy per mol is required to break the second $O-H$ bond?

• A
  $929 \text{ kJ mol}^{-1}$
• B
  $251 \text{ kJ mol}^{-1}$
• C
  $427 \text{ kJ mol}^{-1}$
• D
  $678 \text{ kJ mol}^{-1}$