Assertion (A): Resistivity of a conductor, increases on increasing temperature.
Reason (R): As temperature increases, time between collision decreases.

Options

A. Both (A) and (R) are true and (R) is the correct explanation of (A).
B. Both (A) and (R) are true but (R) is not the correct explanation of (A).
C. (A) is true but (R) is false.
D. (A) is false and (R) is also false.

Explanation

To analyze the given assertion and reason, we can break down the concepts involved step by step.

### Step-by-Step Solution:

1. **Understanding Resistivity**:
- Resistivity (ρ) is a property of a material that quantifies how strongly it resists the flow of electric current. It is influenced by various factors, including temperature.

2. **Effect of Temperature on Resistivity**:
- For most conductors (like metals), resistivity increases with an increase in temperature. This is because, at higher temperatures, the atoms in the conductor vibrate more vigorously, leading to more frequent collisions between the conduction electrons and the vibrating atoms.

3. **Assertion (A)**:
- The assertion states that "Resistivity of a conductor increases on increasing temperature." This statement is true for most conductors, particularly metals.

4. **Understanding the Reason (R)**:
- The reason states that "As temperature increases, the time between collisions decreases." This statement is incorrect. As temperature increases, the time between collisions actually decreases due to increased atomic vibrations, which leads to more collisions.

5. **Evaluating the Assertion and Reason**:
- The assertion is true, but the reason provided is false. Therefore, the correct relationship between the assertion and the reason is that the assertion is true, and the reason is not a valid explanation for the assertion.

### Conclusion:
- **Assertion (A)** is true.
- **Reason (R)** is false.

### Final Answer:
- The assertion is true, and the reason is false.