The ratio of vapour pressures of two liquids A and B in pure state are 1:2. If the two liquids are mixed and the ratio of their mole fraction in vapour phase are 2:1, the liquids A and B were mixed in the ratio of their mole: a)1 : 2 b)2 : 1 c)4 : 1 d)1 : 4

Options

A. `1:2`
B. `2:1`
C. `4:1`
D. `1:4`

Answer

C

Explanation

`P_(A)^0/P_(B)^0=1/2 ("moles fraction of A in vapour phase")/("mole fraction of B vapour phase")=(x_(A)P_(A)^0)/(x_(B)P_(B)^0)=2/1`
Taking ratio, `P_(A)^0/P_(B)^0 // (x_(A)P_(A)^0)/(x_(B)P_(B)^0)=1/2 // 1/2`
`x_(B)/x_(a)=1/4`