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

Solutions with the same osmotic pressure are isotonic Let the molar mass of the substances be M
`pi_1= C_1RT = C_2RT = pi_2`
So, `C_1 = C_2` As density of the solutions are same
so, `(5.25)/M=15/60`
`M = (5.25xx60)/(1.5) = 210.`