The vapour pressure of a solution of a non-volatile electrolyte `B` in a solvent `A` is `95%` of the vapour pressure of the solvent at the same temperature. If the molecular weight of the solvent is `0.3` times, the molecular weight of solute, the weight ratio of the solvent and solute are:

Options

A. 0.15
B. 0.2
C. `4.0`
D. 5.7

Answer

D

Explanation

`p_(s)=95%" of "p^(@), i.e., p_(s)=0.95p^(@)`
`M_(B)=30%" of "M_(A), i.e., M_(B)=0.30M_(A)`
(B = solvent, A = electrolyte)
Applying complete formula
`(p^(@)-p_(s))/(p_(s))=(n_(2))/(n_(1))=(w_(2)//M_(2))/(w_(1)//M_(1))=(w_(2))/(w_(1))xx(M_(1))/(M_(2))=(w_(A))/(w_(B))xx(M_(B))/(M_(A))`
`(p^(@)-0.95p^(@))/(0.95p^(@))=(w_(A))/(w_(B))xx0.30 or (0.05)/(0.95)=(w_(A))/(w_(B))xx0.30`
`"or "(w_(B))/(w_(A))=(0.30xx0.95)/(0.05)=5.7`