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

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

1. A

$90.0\mathrm{g}{\mathrm{mol}}^{-1}$

2. B

$115.0\mathrm{g}{\mathrm{mol}}^{-1}$

3. C

$105.0\mathrm{g}{\mathrm{mol}}^{-}$

4. D

$210.0\mathrm{g}{\mathrm{mol}}^{-1}$

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### Solution:

Isotonic solutions have the same osmotic pressure. Hence, from $\mathrm{\Pi }=cRT$, we get

${c}_{1}={c}_{2}⇒{n}_{1}={n}_{2}$

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