Assuming that water vapour is an ideal gas, the internal energy change ($\Delta U$) when $1\text{mol}$ of water is vapourised at $1\text{bar}$ pressure and $100^{\circ }\text{C}$ is:(Given: Molar enthalpy of vapourization of water at $1\text{bar}$ and $373\text{K}=41{\text{kJ mol}}^{-1}$ and $R=8.3{\text{J mol}}^{-1}{\text{K}}^{-1}$)

1. A
   $4.100{\text{kJ mol}}^{-1}$
2. B
   $3.7904{\text{kJ mol}}^{-1}$
3. C
   $37.904{\text{kJ mol}}^{-1}$
4. D
   $41.00{\text{kJ mol}}^{-1}$