Mole fraction of the toluene in the vapour phase which is in equilibrium with a solution of benzene $(p^0=120torr)$ and toluene$(p^0=80torr)$ having 2.0mole of each is

Question

$\begin{array}{1 1}(a)\;0.40\\(b)\;0.60\\(c)\;0.25\\(d)\;0.50\end{array}$