Benzene and toluene form nearly ideal solution. At `20^(@)C` the vapour pressure of benzene is 75 torr and that of toluene is 22 torr. The partial vapour pressure of benzene at `20^(@)C` for a solution containing 78g of benzene and 46 g of toluene in torr is-

Options

A. 50
B. 25
C. 37.5
D. 53.5

Answer

A

Explanation

No. of moles of benzene in liquid `= ( 78)/( 78)=1 `
No. of moles of toluence in liquid `= ( 46)/(92) = 0.5 `
Mole fraction of benzene `= ( 1)/( 1+ 0.5) =0.666`
Partial vapour pressure of benzene
`= 75 xx 0.666 =49.95~~ 50 `
( torr= mm. of Hg )