Assertion :- Elevation in boiling point and depression in freezing point are colligative properties.
Reason :- All colligative properties are used for the calculation of molecular masses.

Options

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

Explanation

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

### Step 1: Understanding the Assertion
The assertion states that "Elevation in boiling point and depression in freezing point are colligative properties."

**Explanation**:
- Colligative properties are properties that depend on the number of solute particles in a solution, not on the nature of the solute.
- Elevation in boiling point and depression in freezing point are indeed colligative properties because they depend on the concentration of solute particles in a solvent.

### Step 2: Understanding the Reason
The reason states that "All colligative properties are used for the calculation of molecular masses."

**Explanation**:
- It is true that colligative properties can be used to determine molecular masses. However, not all colligative properties are equally suitable for this purpose.
- The most commonly used colligative property for calculating molecular mass is osmotic pressure, while elevation in boiling point and depression in freezing point can also be used but are not as straightforward.

### Step 3: Evaluating the Relationship
Now we evaluate the relationship between the assertion and the reason.
- The assertion is true: elevation in boiling point and depression in freezing point are colligative properties.
- The reason is also true: colligative properties can be used to calculate molecular masses, but it does not correctly explain why the assertion is true.

### Conclusion
- The assertion is true, but the reason does not correctly explain the assertion. Therefore, the correct answer is that the assertion is true, but the reason is false.

### Final Answer:
- Assertion: True
- Reason: False

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