Assertion:Molecular mass of KCl calculated on the basis of colligative properties will be lower than the normal molecular mass.
Reason : Experimentally determined molar mass of always lower than the true value .

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 analyze the given assertion and reason, let's break down the concepts step by step.

### Step 1: Understanding the Assertion
The assertion states that the molecular mass of KCl calculated based on colligative properties will be lower than the normal molecular mass.

**Explanation**:
- Colligative properties depend on the number of solute particles in a solution rather than the identity of the solute.
- When KCl is dissolved in a solvent, it dissociates into two ions: K⁺ and Cl⁻.
- Therefore, the number of particles in the solution is greater than the number of KCl formula units added.
- This increased number of particles leads to a lower calculated molecular mass when using colligative properties (like boiling point elevation or freezing point depression) because the calculations are based on the number of particles, not the original formula unit.

### Step 2: Understanding the Reason
The reason states that the experimentally determined molar mass is always lower than the true value.

**Explanation**:
- This statement is not universally true. The experimentally determined molar mass can be lower than the true value when the solute is an electrolyte (like KCl) in a polar solvent because of dissociation.
- However, this is not the case for all solutes. For non-electrolytes or in non-polar solvents, the experimentally determined molar mass can be equal to or even higher than the true value.

### Step 3: Conclusion
- The assertion is true because KCl dissociates into K⁺ and Cl⁻, leading to a lower calculated molecular mass based on colligative properties.
- The reason is false because it generalizes the behavior of all solutes without considering the nature of the solute and solvent.

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