At constant temperature , in a closed vessel, an ideal solution is formed by liquid-A and liquid -B and mole fraction of A and B are0.6 and 0.4 respectively. If vapour pressure of pure liquids are 125.0 and 62.5 mm respectively, then their mole fraction in vapour state are respectively ( In vessel, no other component is in gaseous form. )

Options

A. 0.6 and 0.4
B. 0.4 and 0.6
C. 0.25 and 0.75
D. 0.75 and 0.25

Answer

D

Explanation

`P_(A)= P_(A)^(0)xxX_(A)= 125 xx 0.6 = 75 mm`
`P_(B)=P_(B)^(0) xxX_(B) = 62.5 xx 0.4 = 25 mm`
`P("total") = P_(A) + P_(B) =75+25 = 100mm`
`P_(A) = P_("total ") xxY_(A)`
`:. 75 = 100xx Y_(A)` `:. Y_(A) = 0.75 `
Similarly `:. Y_(B) = 0.251`