Benzene and toluene form nearly ideal solutions. 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 78 g of benzene and 46 g of toluene in torr is

Options

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

Answer

A

Explanation

Molecular mass of benzene `(C_H_6) = 78`
No. of moles of benzene `=78/78 =1`
Molecular mass of toluene `(C_6H_5 - CH_3) = 92`
No. of moles of toluene `= 46/92= 0.5`
`X_("Benzene") =1/(1+0.5)=2/3`
`P_("Benzene")= P_("Benzene")^@ xx X_("Benzene") = 75 xx2/3 = 50` torr