Question

The vapour pressure of pure liquid A is `10` torr and at the same temperature when `1` g solid B is dissolved in `20`g of A , its vapour pressure is reduced to`9.0`torr . If the molecular mass of A is `200`amu , then the molecular mass of B is
A. `100`amu
B. `90`amu
C. `75`amu
D. `120`amu

Answer 1

Correct Answer - B
`(10-9)/(10)=((1)/(8))/((1)/(x)+(20)/(200))`
`(1)/(10)=(1)/((x)/((1)/(x)+(1)/(10)))=(10)/(x+10)rArr x=90`