The vapour pressure of a solution of 5g of non-electrolyte in 100g of water at a particular temperature is `2985 N m^(-2)`. The vapour pressure of pure water at that temperature is `3000 N m^(-2)`. The molecular weight of the solute is

Options

A. 180
B. 90
C. 270
D. 200

Answer

A

Explanation

`(p_(1)^(@)-P)/P_(1)^(@)=(W_(2)//M_(2))/(W_(1)//M_(1)+W_(2)//M_(2))`
`=(34.2//342)/(34.2//342+180//18)=0.1/10.1=0.0099`
i.e., ` (3000-2985)/3000=(15//M_(2))/(100//18) or M_(2) =180`