Assertion : In photon-particle collision the total energy and total momentum are conserved. Reason : The number of photons are conserved in a collision.

Options

A. If both assertion and reason are true and reason is the correct explanation of assertion.
B. If both assertion and reason are true but reason is not the correct explanation of assertion.
C. If assertion is true but reason is false.
D. If both assertion and reason are false.

Explanation

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

### Step 1: Understand the Assertion
The assertion states that in a photon-particle collision, the total energy and total momentum are conserved.

- **Explanation**: In any collision, including photon-particle collisions (like photon-electron collisions), the laws of conservation of energy and momentum apply. This means that the total energy before the collision is equal to the total energy after the collision, and the same applies for momentum.

### Step 2: Understand the Reason
The reason states that the number of photons is conserved in a collision.

- **Explanation**: This statement is not necessarily true. In photon-particle collisions, photons can be absorbed by particles (like electrons), or new photons can be emitted. Therefore, the number of photons can change during the collision process.

### Step 3: Conclusion
Based on the analysis:
- The assertion is true: Total energy and total momentum are conserved in photon-particle collisions.
- The reason is false: The number of photons is not conserved in such collisions.

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