The vapour pressure of pure benzene at a certain temperature is 0.850 bar. A non-volatile, non-electrolye solid weighing 0.5 g is added to 39.0 g of benzene (molar mass 78 g/mol). The vapour pressure of the solution then is 0.845 bar. What is the molecular mass of the solid substance?
(a) 58
(b) 180
(c) 170
(d) 145
