Molar mass of \(CH_2Cl_2\,=\,85\,g/mol.\)

Molar of \(CHCl_3\,=\,\frac {11.95}{119.5}\,=\,0.1\,mol.\)

Molar of \(CH_2Cl_2\,=\,\frac {8.5}{85}\,=\,0.1\,mol.\)

Mole fraction of \(CHCl_3\,=\,\frac {0.1}{0.2}\,=\,0.5\,mol\)

Mole fraction of \(CH_2Cl_2\,=\,\frac {0.1}{0.2}\,=\,0.5\,mol\)

(Given-

Vapour pressure of \(CHCl_3\,=\,200\,mm\)  \(Hg\,=\,0.263\,atm\).

Vapour pressure of \(CH_2Cl_2\,=\,415\,mm\)  \(Hg\,=\,0.546\,atm\).)

\((1\,atm\,=\,760\,mm\,Hg)\)

\(\therefore P_{(abovesolution)}\) \(=\) Mole fractiion of \(CHCl_3\times \) (Vapour pressure of \(CHCl_3\) ) \(+\) Mole fractiion of \(CH_2Cl_2\times \) (Vapour pressure of \(CH_2Cl_2\) )

\(=\,0.5\times 0.263\,+\,0.5\times 0.546\,=\,0.4045\)

Mole fraction of \(CHCl_3\) in vapour form

\(=\,\frac {0.1315}{0.4045}\,=\,0.325\)