Assertion : Distance between two particles moving with consant velocities always remains constant.
Reason : In the above case, relative motion between them is uniform.

Options

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

Explanation

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

### Step 1: Understand the Assertion
The assertion states that "the distance between two particles moving with constant velocities always remains constant."

- **Analysis**: This statement is not necessarily true. If two particles are moving in the same direction with the same velocity, the distance between them will remain constant. However, if they are moving in different directions or at different speeds, the distance between them will change over time. Therefore, the assertion is **false**.

### Step 2: Understand the Reason
The reason states that "in the above case, relative motion between them is uniform."

- **Analysis**: Relative motion refers to the motion of one object as observed from another object. If both particles are moving with constant velocities, the relative velocity (the difference in their velocities) is also constant. This means that their relative motion is uniform. Therefore, the reason is **true**.

### Step 3: Conclusion
Now we can conclude the relationship between the assertion and the reason:

- The assertion is false because the distance between two particles moving with constant velocities does not always remain constant.
- The reason is true because if both particles are moving with constant velocities, their relative motion is uniform.

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