A : If temperature does not affect the rate of reaction , `E_a=0`
R : Lesser the activation energy, slower will be the reaction.

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 statements in the question, we will break down the assertion (A) and the reason (R) step by step.

### Step 1: Understand the Assertion
**Assertion (A)**: If temperature does not affect the rate of reaction, then \(E_a = 0\).

- The assertion states that if the temperature has no effect on the rate of a reaction, then the activation energy (\(E_a\)) must be zero.
- The activation energy is the minimum energy required for a reaction to occur. If temperature changes do not affect the rate, it implies that the energy barrier for the reaction is nonexistent, leading to the conclusion that \(E_a\) is zero.

### Step 2: Understand the Reason
**Reason (R)**: Lesser the activation energy, slower will be the reaction.

- This statement suggests that a lower activation energy results in a slower reaction, which contradicts the fundamental principles of chemical kinetics.
- In reality, a lower activation energy generally means that more molecules have enough energy to overcome the energy barrier, leading to a faster reaction. Thus, this statement is false.

### Step 3: Evaluate the Truth of Each Statement
- **Assertion (A)** is true because if temperature does not affect the rate of reaction, it implies that the activation energy must be zero.
- **Reason (R)** is false because a lower activation energy actually leads to a faster reaction, not a slower one.

### Conclusion
Based on the evaluations:
- The assertion is true.
- The reason is false.

Therefore, the correct answer to the question is that the assertion is true, but the reason is false.

### Final Answer
The correct option is **3: Assertion is true, but reason is false**.

---