Assertion: In Down's process `CaCI_(2)` and `NaF` is added with fused `NaCI`
Reason: `CaCI_(2)` and `NaF` lower down melting point of NaCI

Options

A. If both Assertion & Reason are True & the Reason is a correct explanation of the Assertion
B. If both Assertion & Reason are True but Reason is not a correct explanation of the Assertion
C. If Assertion is True but the Reason is False
D. If both Assertion & Reason are False

Answer

To solve the question regarding the assertion and reason related to Down's process, we can break it down into clear steps.

### Step-by-Step Solution:

1. **Understand Down's Process**:
- Down's process is a method used to obtain sodium metal through the electrolysis of molten sodium chloride (NaCl).

**Hint**: Remember that Down's process specifically involves the electrolysis of molten NaCl to produce sodium metal.

2. **Identify the Assertion**:
- The assertion states that in Down's process, calcium chloride (CaCl₂) and sodium fluoride (NaF) are added to fused NaCl.

**Hint**: Focus on what materials are involved in the Down's process and their roles.

3. **Identify the Reason**:
- The reason provided is that CaCl₂ and NaF lower the melting point of NaCl.

**Hint**: Consider the significance of lowering the melting point in the context of the process.

4. **Melting Point of NaCl**:
- The melting point of pure NaCl is approximately 1080 K. This high melting point can make the electrolysis process inefficient.

**Hint**: Recall the melting point of NaCl and how it affects the electrolysis process.

5. **Effect of Additives**:
- By adding CaCl₂ and NaF, the melting point of the mixture is lowered to about 850 K. This reduction is crucial because it allows the electrolysis to occur at a lower temperature, making the process more efficient.

**Hint**: Think about why lowering the melting point is beneficial for the electrolysis of NaCl.

6. **Volatility of Sodium**:
- At the higher temperature of 1080 K, sodium (Na) produced during electrolysis is volatile and can vaporize, leading to loss of product. Lowering the temperature helps in retaining the sodium metal.

**Hint**: Consider the implications of sodium's volatility at different temperatures.

7. **Conclusion**:
- Both the assertion and reason are correct. The assertion correctly states the use of CaCl₂ and NaF in Down's process, and the reason correctly explains why these substances are added (to lower the melting point of NaCl). Therefore, the reason is a correct explanation of the assertion.

**Hint**: Summarize the relationship between the assertion and reason to conclude their correctness.

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