Assertions : When HCl gas is passed through a saturated solution of common salt, pure NaCl is precipitated.
Reason: The solubility product of NaCl gets lowered.

Options

A. If both Assertion and Reason are CORRECT and a Reason is the CORRECT explanations of the Assertion
B. If both Assertion and Reason are CORRECT but Reason is not CORRECT explanation of the Assertion.
C. If Assertion is CORRECT but Reason is INCORRECT.
D. If Assertion is INCORRECT but Reason is CORRECT.

Answer

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

**Assertion:** When HCl gas is passed through a saturated solution of common salt, pure NaCl is precipitated.

**Reason:** The solubility product of NaCl gets lowered.

### Step-by-Step Solution:

1. **Understanding the Dissociation of NaCl:**
- NaCl dissociates in solution into Na⁺ and Cl⁻ ions.
- The solubility product (Ksp) of NaCl can be expressed as:
\[ K_{sp} = [Na^+][Cl^-] \]

2. **Dissociation of HCl:**
- HCl dissociates in solution into H⁺ and Cl⁻ ions.
- When HCl gas is passed through the saturated NaCl solution, it increases the concentration of Cl⁻ ions in the solution.

3. **Common Ion Effect:**
- The increase in Cl⁻ concentration due to the addition of HCl is an example of the common ion effect.
- According to Le Chatelier's principle, adding a common ion (Cl⁻ in this case) will shift the equilibrium to the left, favoring the formation of solid NaCl.

4. **Ionic Product vs. Solubility Product:**
- The ionic product (IP) is calculated as:
\[ IP = [Na^+][Cl^-] \]
- When Cl⁻ concentration increases, the ionic product can exceed the solubility product (Ksp) of NaCl.
- If \( IP > K_{sp} \), precipitation of NaCl occurs.

5. **Conclusion on the Assertion:**
- Since the assertion states that pure NaCl is precipitated when HCl is passed through the saturated NaCl solution, this is correct because the increase in Cl⁻ concentration leads to precipitation.

6. **Conclusion on the Reason:**
- The reason states that the solubility product of NaCl gets lowered. However, the Ksp itself does not change; rather, the conditions under which NaCl can remain dissolved change due to the increased concentration of Cl⁻.
- Therefore, while the precipitation occurs, the statement about the Ksp getting lowered is misleading. The Ksp remains constant at a given temperature.

### Final Answer:
Both the assertion and reason are correct, but the reason does not correctly explain the assertion. Thus, the correct conclusion is that the assertion is true, but the reason is not the correct explanation for the assertion.