A : At constant volume on increasing temperature the collision frequency increases.
R : Collision frequency `prop` temperature of gas.

Options

A. If both Assertion & Reason are true and the reason is the correct explanation of the assertion, then Mark (1)
B. If both Assertion & Reason are true but the reason is not the correct explanation of the assertion, then mark (2)
C. If Assertion is true statement but Reason is false, then mark (3)
D. If both Assertion and Reason are false statements, then mark (4).

Answer

To solve the question regarding the assertion and reason about collision frequency and temperature, we will analyze each statement step by step.

### Step-by-Step Solution:

1. **Understanding the Assertion (A)**:
- The assertion states: "At constant volume, on increasing temperature, the collision frequency increases."
- To analyze this, we recognize that increasing the temperature of a gas increases the kinetic energy of its particles.

**Hint**: Consider how temperature affects the energy and motion of gas particles.

2. **Kinetic Energy and Velocity**:
- As the temperature increases, the average kinetic energy of the gas particles increases.
- The kinetic energy (KE) of a particle is given by the formula:
\[ KE = \frac{1}{2} mv^2 \]
- Therefore, if kinetic energy increases, the velocity (v) of the particles must also increase.

**Hint**: Recall the relationship between kinetic energy, mass, and velocity.

3. **Collision Frequency**:
- Collision frequency is defined as the number of collisions per unit time.
- With an increase in velocity, the likelihood of particles colliding with each other also increases because they are moving faster.

**Hint**: Think about how faster-moving particles interact with each other.

4. **Constant Volume Condition**:
- The assertion specifies that this occurs at constant volume.
- If the volume is constant, the increase in temperature leads to an increase in pressure, but the number of particles in a given volume remains the same.

**Hint**: Consider how volume impacts the space available for collisions.

5. **Conclusion on Assertion**:
- Since increasing temperature leads to increased kinetic energy and thus increased velocity, which in turn increases collision frequency, the assertion is **true**.

6. **Understanding the Reason (R)**:
- The reason states: "Collision frequency is directly proportional to the temperature of gas."
- While it is true that temperature affects collision frequency, it is not the only factor. Collision frequency also depends on the number of particles and the volume of the gas.

**Hint**: Reflect on other factors that might influence collision frequency.

7. **Conclusion on Reason**:
- Since collision frequency is influenced by multiple factors (not just temperature), the reason is **false**.

8. **Final Evaluation**:
- The assertion is true, but the reason is false. Therefore, the correct option is that the assertion is true and the reason is false.

### Final Answer:
- Assertion (A) is **True**.
- Reason (R) is **False**.