A 5.25% solution of a substance is isotonic with a 1.5% solution of urea ( molar mass `= 60g mol^(-1) `) in the same solvent. If the densities of both the solutions are assumed to be equal to `1.0 g cm^(-3)`, molar mass of the substance will be

Options

A. `90.0 g mol^(-1)`
B. `115.0 g mol^(-1)`
C. `105.0 g mol^(-1)`
D. `210.0 g mol^(-1)`

Answer

D

Explanation

`pi_(Unk) = pi_("Unea")`
`(W_(1))/(M_(1)U) = (W_(2))/(M_(2)U)`
`(5.25)/(M_(1)) = (1.5)/(60)`
`M_(1) = 210 gm//mol`