(A) the trajetory traced by an incident particle depends on the impact parameter of collision.
(R) the impact parameter is the perpendicular distance of the initial velocity vector of the incident particle from the centre of the target nucleus.

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

### Step-by-Step Solution:

1. **Understanding the Assertion**:
- The assertion states that "the trajectory traced by an incident particle depends on the impact parameter of the collision."
- This means that how the particle moves after colliding with the nucleus is influenced by how far away (the impact parameter) it was from the center of the nucleus when it approached.

2. **Understanding the Reason**:
- The reason states that "the impact parameter is the perpendicular distance of the initial velocity vector of the incident particle from the center of the target nucleus."
- This is a definition of the impact parameter, which is indeed a crucial concept in understanding collisions in nuclear physics.

3. **Analyzing the Impact Parameter**:
- To visualize this, we can consider a diagram where we have a target nucleus and incident particles approaching it at different distances.
- The impact parameter (b) is the shortest distance from the center of the nucleus to the line along which the particle is moving.

4. **Comparing Trajectories**:
- If we have two particles, one with a larger impact parameter (b1) and another with a smaller impact parameter (b2), we can see that:
- The particle with the larger impact parameter will experience less deflection and will have a trajectory that is closer to a straight line.
- Conversely, the particle with the smaller impact parameter will be deflected more significantly due to the stronger influence of the nuclear force.

5. **Conclusion**:
- Therefore, the assertion is true: the trajectory does depend on the impact parameter.
- The reason is also true, as it correctly defines the impact parameter.
- However, the reason does not explain why the assertion is true; it merely states what the impact parameter is without linking it to the trajectory's dependence.

### Final Answer:
- Both the assertion and the reason are true, but the reason is not the correct explanation for the assertion.