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 solve the question, we need to analyze both the assertion and the reason provided.

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

- According to the Arrhenius equation, the rate constant \( k \) is given by:
\[ k = A e^{-\frac{E_a}{RT}} \]
where:
- \( A \) is the pre-exponential factor,
- \( E_a \) is the activation energy,
- \( R \) is the gas constant,
- \( T \) is the temperature.

- If the temperature does not affect the rate of reaction, it implies that the rate constant \( k \) is not changing with temperature.

- For \( k \) to remain constant regardless of temperature, the term \( e^{-\frac{E_a}{RT}} \) must be equal to 1. This occurs when:
\[ -\frac{E_a}{RT} = 0 \implies E_a = 0 \]

- Therefore, the assertion is **True**.

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

- From the Arrhenius equation, we can see that \( k \) (the rate constant) is inversely proportional to the activation energy \( E_a \):
\[ k \propto e^{-\frac{E_a}{RT}} \]

- A lower \( E_a \) means a larger value of \( k \), which leads to a faster rate of reaction. Hence, the statement "lesser the activation energy, slower will be the reaction" is incorrect.

- Therefore, the reason is **False**.

### Conclusion
- The assertion is **True**.
- The reason is **False**.

### Final Answer
The correct option is that the assertion is true, but the reason is false.

---