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_(o)-P_(s))/(P_(o))=(w)/(m)xx(M)/(W) " " : RLVP = (w)/(m)xx(M)/(W)`,
`m=(w)/(m)xx(1000)/(W), " " 0.0125=(w)/(m)xx(1000)/(W)xx(M)/(100)`
`0.0125xx1000=((w)/(m)xx(1000)/(W))M`
`M xx m = 125 " " (M=18)`
`m xx M =0.0125xx1000=12.5`
`m=(12.5)/(M)=(12.5)/(18)=0.6944 =0.70`