Assertion : The molality of the solution does not change with change in temperature.
Reason : The molality is expressed in units of moles per 1000 g of solvent.

Options

A. If both assertion and reason are true and reason is the correct explanation of assertion
B. If both assertion and reason are true but reason is not the correct explanation of assertion
C. If assertion is true but reason is false
D. If both assertion and reason are false.

Explanation

To solve the question, we need to analyze both the assertion and the reason provided.

### Step-by-Step Solution:

1. **Understanding the Assertion**:
- The assertion states that "The molality of the solution does not change with change in temperature."
- **Explanation**: Molality (m) is defined as the number of moles of solute per kilogram of solvent. It is given by the formula:
\[ \text{Molality (m)} = \frac{\text{moles of solute}}{\text{mass of solvent in kg}} \]
- Since molality is based on the mass of the solvent (which is in kilograms), it does not change with temperature. This is because mass remains constant regardless of temperature changes.

**Hint**: Remember that molality is defined in terms of mass, which does not vary with temperature.

2. **Understanding the Reason**:
- The reason states that "The molality is expressed in units of moles per 1000 g of solvent."
- **Explanation**: This is correct because 1 kg of solvent is equivalent to 1000 g. Therefore, molality can indeed be expressed as:
\[ \text{Molality (m)} = \frac{\text{moles of solute}}{1000 \text{ g of solvent}} \]
- This reinforces the assertion because it highlights that molality is based on the mass of the solvent, which does not change with temperature.

**Hint**: Recognize that the unit conversion from kg to g does not affect the fundamental nature of molality.

3. **Conclusion**:
- Both the assertion and the reason are true.
- The reason correctly explains the assertion because it clarifies that the definition of molality relies on the mass of the solvent, which is unaffected by temperature changes.

### Final Answer:
Both the assertion and the reason are true, and the reason is the correct explanation of the assertion.

### Correct Option:
The correct answer is option 1: Both the assertion and the reason are true, and the reason is the correct explanation of the assertion.