A : A positive catalyst increases the rate of reaction .
R : A positive catalyst alters reaction mechanism and decreases activation energy.

Options

A. If both Assertion & Reason are true and the reason is the correct explanation of the assertion , then mark (1).
B. If both Assertion & Reason are true but the reason is not the correct explanation of the assertion , then mark (2).
C. If Assertion is true statement but Reason is false, then mark (3).
D. If both Assertion and Reason are false statements , then mark (4)

Answer

To analyze the given assertion and reason, we will break down the concepts of catalysts, specifically positive catalysts, and their effects on reaction rates and mechanisms.

### Step-by-Step Solution:

1. **Understanding the Assertion (A)**:
- The assertion states that "A positive catalyst increases the rate of reaction."
- This is true because a positive catalyst provides an alternative pathway for the reaction, which leads to an increase in the rate of reaction.

2. **Understanding the Reason (R)**:
- The reason states that "A positive catalyst alters the reaction mechanism and decreases activation energy."
- This is also true. A positive catalyst changes the reaction mechanism by providing a different pathway that has a lower activation energy compared to the uncatalyzed reaction.

3. **Connecting Assertion and Reason**:
- The reason explains how a positive catalyst increases the rate of reaction. By decreasing the activation energy, the catalyst allows more reactant molecules to have sufficient energy to overcome the energy barrier, thus increasing the rate of the reaction.

4. **Conclusion**:
- Both the assertion and the reason are true, and the reason is indeed the correct explanation for the assertion.

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

---