The molal elevation/depression constant depends upon -

Options

A. `DeltaH_("solution")`
B. Nature of solvent
C. Nature of solute
D. Freezing point of solution

Answer

To solve the question regarding the factors on which the molal elevation/depression constant depends, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Concept**:
- The molal elevation constant (K_b) and the molal depression constant (K_f) are properties that relate to how the boiling point or freezing point of a solvent changes when a solute is added.

2. **Identifying the Relationships**:
- The change in freezing point (ΔT_f) can be expressed as:
\[ \Delta T_f = K_f \cdot m \]
- The change in boiling point (ΔT_b) can be expressed as:
\[ \Delta T_b = K_b \cdot m \]
- Here, \(m\) is the molality of the solution.

3. **Analyzing the Constants**:
- From the equations, we see that K_f and K_b are constants that depend on the solvent used, not on the solute or the specific conditions of the solution.

4. **Evaluating the Options**:
- **Option A (ΔH of solution)**: This refers to the enthalpy change when a solute dissolves. It does not affect the molal constants.
- **Option B (Nature of solvent)**: This is correct. K_f and K_b depend solely on the solvent.
- **Option C (Nature of solute)**: The properties of the solute do not affect K_f or K_b.
- **Option D (Freezing point of solution)**: The freezing point itself does not determine the value of K_f.

5. **Conclusion**:
- The molal elevation/depression constant depends only on the nature of the solvent. Therefore, the correct answer is **Option B: Nature of solvent**.

### Final Answer:
The molal elevation/depression constant depends upon the **nature of solvent**.