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

Answer

A

Explanation

Isotonic solutions have the same molar concentration. Hence
`(52.5"g L"^(-1))/(M)=("15 g L"^(-1))/("60 g mol"^(-1))`
(100g solution = 100 mL as `d = 1 g mL^(-1)`)
`M=(52.5xx60)/(15)=210"g mol"^(-1)`.