When `3`g of a novolatile solute is dissolved in 50 g of water , the relative lowering of vapour pressure observed is `0.018 Nm^(-2)`. Molecular weight of the substances is

Options

A. `60`
B. `30`
C. `40`
D. `120`

Answer

A

Explanation

`(P_(A)^(@)-P)/(P_(A)^(@))=chi_(B),`
By putting values `0.018=((w_(B))/(M_(B)))/(w_(A)/(w_(B))+(w_(B))/(M_(B)))`
`rArr 0.018=((3)/(M_(B)))/((3)/(M_(B))+(50)/(18))`
by calculating `M_(B)~~60`