Question

The V.P of pure liquid A is 0.60 torr. On adding a non-volatile solid B to A, its
V.P decreases by 0.20 torr. The mole fraction of solvent A in the solution is
a) 0.1 b) 0.33 C) 0.66 d) none of these​

Answer 1

relative lowering of vapour pressure/ vapour pressure of pure solvent = Mole fraction of solute

0.6-0.2/0.6=0.4/0.6= 4/6 = 2/3

but they asked Mole fraction of solvent hence 1-2/3= 1/3= 0.333 hence the option is b