\(\frac{{\Delta p}}{{{p^o}}}\, = \,\frac{n}{{n + N}}\)  (Mole fraction of solute)

\(\frac{{10}}{{{p^o}}}\, = \,0.2\,\,\therefore \,{p^o}\, = \,50\,\,mm\,Hg\)

For other solution of same solvent

\({\frac{{20}}{{{p^o}}}\, = \frac{n}{{n + N}}}\) (Mole fraction of solute)

\( \Rightarrow \,\frac{{20}}{{50}}\, = \) Mole fraction of solute

\( \Rightarrow \) Mole fraction of solute \(=\,0.4\)

As Mole fractionof solute \(+\) Mole fraction of solvent \(=\,1\)

Hence, Mole fraction of solvent \(=\,1-0.4\,=\,0.6\)