Assertion : A particle is moving on a straight line with a uniform velocity, its angular momentum is always zero.
Reason : The momentum is zero when particle moves with a uniform velocity

Options

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

Explanation

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

### Step-by-Step Solution:

1. **Understanding the Assertion**:
- The assertion states that if a particle is moving in a straight line with uniform velocity, its angular momentum is always zero.
- Angular momentum (L) is defined as \( L = R \times P \), where \( R \) is the position vector from the point about which we are calculating the angular momentum to the particle, and \( P \) is the linear momentum of the particle.

2. **Analyzing Angular Momentum**:
- The linear momentum \( P \) of the particle is given by \( P = mv \) (where \( m \) is the mass and \( v \) is the velocity).
- The angular momentum can be expressed as \( L = R \times mv \).
- The value of \( L \) depends on the perpendicular distance from the line of motion of the particle to the point about which we are calculating the angular momentum.

3. **Determining When Angular Momentum is Zero**:
- Angular momentum will be zero if the point about which we are calculating it lies on the line of motion of the particle. In this case, the perpendicular distance \( R_{\perpendicular} \) becomes zero, leading to \( L = mv \cdot 0 = 0 \).
- However, if the point is not on the line of motion, the angular momentum will not be zero as there will be a non-zero perpendicular distance.

4. **Conclusion about the Assertion**:
- The assertion is false because it claims that angular momentum is always zero, which is not true. It depends on the reference point chosen.

5. **Understanding the Reason**:
- The reason states that momentum is zero when a particle moves with uniform velocity.
- This statement is incorrect. A particle moving with uniform velocity has non-zero momentum, given by \( P = mv \) (where \( v \) is not zero).

6. **Conclusion about the Reason**:
- The reason is also false because it incorrectly states that momentum is zero for a particle moving with uniform velocity.

### Final Conclusion:
Both the assertion and the reason are false. Therefore, the correct answer to the question is that both the assertion and the reason are false.