Two liquids A and B form an ideal solution. At 320 K, the vapour pressure of the solution, containing 3 mol of A and 1 mol of B is 500 mm Hg. At the…

Two liquids A and B form an ideal solution. At $\displaystyle 320$ K , the vapour pressure of the solution, containing $\displaystyle 3$ mol of $\displaystyle A$ and $\displaystyle 1$ mol of $\displaystyle B$ is $\displaystyle 500$ mm Hg . At the same temperature, if $\displaystyle 1$ mol of A is further added to this solution, vapour pressure of the solution increases by $\displaystyle 20$ mm Hg . Vapour pressure (in mm Hg ) of B in pure state is $\displaystyle \_\_\_\_$. (Nearest integer)