The relative lowering of vapour pressure of an aqueous solution containing a non-volatile solute, is 0.0125. The molality of the solution is

Explanation

`(P_(A)^(@)-P_("solution"))/(P_(A)^(@))=0.0125=x_(B)=(n_(B))/(n_(A)+n_(B)), :. x_(A)=0.9875=(n_(A))/(n_(A)+n_(B))`
`(n_(B))/(n_(A))=1/79, m=(n_(B))/(w.t. "of solvent"(kg))=(n_(B))/((n_(A)xx"molar mass of solvent")xx10^(-3))`
`=1/(79xx18xx10^(-3))~~0.70`