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

Options

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

Answer

D

Explanation

Solution with the same osmotic pressure are isotonic Let the molar mass of the substance be M
`pi_(1)=C_(1)RT=C_(2)RT=pi_(2)`
`so,C_(1)=C_(2)`
As density of the solution are same
So,`(5.25)/(M)=(15)/(60)`
`:.M=(5.25xx60)/(1.5)=210`