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 g mol"^(-1)`

Answer

A

Explanation

Isotonic solutions have the same molar concentration. Hence,
Molar conc. Of the substance = Molar conc. Of urea
`(52.5gL^(-1))/(M)=(15gL^(-1))/("60 g mol"^(-1))`
`("100 g solution = 100 mL as d = 1 g mL"^(-1))`
`therefore" "M=(52.5xx60)/(15)="210 g mol"^(-1)`