Which of the following statements is correct ?

Options

A. A saturated solution will remain saturated at all temperatures.
B. A plant cell swells when placed in hypertonic solution
C. The depression in freezing point is directly proportional to molality of the solution
D. Lowering in vapour pressure is a colligative property .

Explanation

To determine which of the statements is correct, let's analyze each statement one by one:

1. **A saturated solution will remain saturated at all temperatures.**
- This statement is incorrect. The solubility of a solute typically changes with temperature. Generally, as the temperature increases, the solubility of most solids in liquids increases. Therefore, a saturated solution may not remain saturated at all temperatures.

2. **A plant cell swells when placed in a hypertonic solution.**
- This statement is also incorrect. A hypertonic solution has a higher concentration of solute compared to the inside of the plant cell. As a result, water moves out of the cell to balance the solute concentration, causing the plant cell to shrink, not swell.

3. **The depression in freezing point is directly proportional to the molality of the solution.**
- This statement is correct. The depression in freezing point (ΔTf) is indeed directly proportional to the molality (M) of the solution, as described by the formula: ΔTf = Kf * M, where Kf is the freezing point depression constant. This means that as the molality of the solution increases, the depression in freezing point also increases.

4. **Lowering in vapor pressure is a colligative property.**
- This statement is partially correct but misleading. While lowering of vapor pressure is related to colligative properties, it is specifically the "relative lowering of vapor pressure" that is considered a colligative property. Therefore, the statement as it stands is not entirely accurate.

Based on the analysis above, the correct statement is:

**The depression in freezing point is directly proportional to the molality of the solution.**