The boiling point of `0.2 mol kg^(-1)` solution of `X` in water is greater than equimolal solution of `Y` in water. Which 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 Y.
C. Molecular mass of X is less than the molecular mass of Y.
D. Y is undergoing dissociation in water while X undergoes no change.

Explanation

To solve the question, we need to analyze the information given about the boiling points of the solutions and the implications of colligative properties.

### Step-by-Step Solution:

1. **Understanding the Problem**: We have two solutions: one is a 0.2 mol/kg solution of substance X in water, and the other is an equimolar solution of substance Y in water. We know that the boiling point of the solution containing X is greater than that of the solution containing Y.

2. **Colligative Properties**: The boiling point elevation of a solution is a colligative property, which means it depends on the number of solute particles in the solution, not the identity of the solute. The formula for boiling point elevation is:
\[ \Delta T_b = i \cdot K_b \cdot m \]
where \( \Delta T_b \) is the boiling point elevation, \( i \) is the van 't Hoff factor (which represents the number of particles the solute dissociates into), \( K_b \) is the ebullioscopic constant of the solvent, and \( m \) is the molality of the solution.

3. **Comparing the Solutions**: Since both solutions have the same molality (0.2 mol/kg), the difference in boiling point must be due to the van 't Hoff factor \( i \). If the boiling point of the solution of X is greater, it indicates that \( i \) for X must be greater than \( i \) for Y.

4. **Implications of Dissociation**: A higher value of \( i \) suggests that substance X is dissociating into more particles in solution than substance Y. This means that substance X is likely an electrolyte (which dissociates into ions), while substance Y may be a non-electrolyte (which does not dissociate).

5. **Conclusion**: Based on the analysis, the correct statement is that "X is undergoing dissociation in water." This explains why the boiling point of the solution of X is greater than that of Y, as the dissociation increases the number of solute particles, leading to a higher boiling point elevation.

### Final Answer:
The true statement is: **X is undergoing dissociation in water.**