At T ( K ) , the vapour pressure of pure benzene (molar mass =78 ~g ~mol ⁻¹ ) is 0.85 bar . When 2.0 ~g of non-volatile, non-electrolyte solute is added to 39 ~g of benzene, the vapour pressure of solution at T ( K ) is 0.83 bar. The elevation in boiling point (in K ) of the same solution is: ( K _ b . of benzene is 2.6 ~K ~kg ~mol ⁻¹ )