Assertion : Thermite mixture `Fe_(2)O_(3) +Al` (powder) is used in the welding.
Reason : Al is a good reductant.

Options

A. If both assetion and reason are CORRECT, and reason is the CORRECT explanation of the assertion
B. If both assertion and reason are CORRECT, but reason is NOT the 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 regarding the assertion and reason, we will analyze both statements and determine their validity and relationship.

### Step-by-Step Solution:

1. **Understanding the Assertion**:
- The assertion states that the thermite mixture \( \text{Fe}_2\text{O}_3 + \text{Al} \) (aluminum powder) is used in welding.
- This is true because the thermite reaction produces molten iron and aluminum oxide when aluminum reduces iron(III) oxide. The heat generated from this reaction is used in welding processes.

2. **Understanding the Reason**:
- The reason given is that aluminum is a good reductant.
- This is also true. Aluminum is indeed a strong reducing agent and can reduce metal oxides to metals.

3. **Analyzing the Relationship**:
- While both the assertion and reason are correct, we need to determine if the reason is the correct explanation for the assertion.
- The assertion is based on the thermite reaction's exothermic nature, which provides the necessary heat for welding. The reason provided (that aluminum is a good reductant) does not directly explain why the thermite mixture is used in welding; rather, it is the heat produced from the reaction that is the key factor.

4. **Conclusion**:
- Therefore, both the assertion and reason are correct, but the reason does not correctly explain the assertion.
- The correct option is that both assertion and reason are correct, but the reason is not the correct explanation of the assertion.

### Final Answer:
- **Option 2**: Both assertion and reason are correct, but reason is not the correct explanation of assertion.