### Neet Solved Paper 2015 Question 22

##### Question: The boiling point of $ 0.2molk{g^{-1}} $ solution of X in water is greater than equimolal solution of Y in water. Which one of the following statements is true in this case?

#### Options:

A) X is undergoing dissociation in water.

B) Molecular mass of X is greater than the molecular mass of V.

C) Molecular mass of X is less than the molecular mass of V.

D) V is undergoing dissociation in water while X undergoes no change,

## Show Answer

#### Answer:

Correct Answer: A

#### Solution:

Molality of solution X = molality of solution Y = 0.2mol/kg

We know that, elevation in the boiling point $ (\Delta T _{b}) $ of a solution is proportional to the molal concentration of the solution

i.e. $ \Delta T _{b}\propto m,or,\Delta T _{b}=K _{b}m $ where, m is the molality of the solution and $ K _{b} $ is molal boiling point constant or ebullioscopic constant.

$ \therefore $ By elevation in boiling point relation $ \Delta {\tau_b}=iK _{b}mor,\Delta {T_b}\propto i $ where, $ i $ is van’t Hoff is factor

Since, $ \Delta T _{b} $ , of solution X is greater than $ \Delta T _{b} $ of solution Y. (Observed colligative property is greater than normal colligative property).

$ \therefore $ $ i $ of solution $ X>i $ of solution Y

$ \therefore $ Solution X undergoing dissociation.