Extent of physisorption of a gas increases with ………. .

Options

A. increase in temperature
B. decrease in temperature
C. decrease in surface area of adsorption
D. decrease in strength of van der Waals forces.

Explanation

To solve the question regarding the extent of physisorption of a gas, we need to understand the factors that influence physisorption. Let's break down the solution step by step.

### Step-by-Step Solution:

1. **Understanding Physisorption**:
- Physisorption is the process where gas molecules adhere to a solid surface through weak Van der Waals forces. This type of adsorption is characterized by its reversibility and is not specific to any particular gas.

2. **Characteristics of Physisorption**:
- It arises due to weak Van der Waals forces.
- It is not specific in nature.
- It is reversible.
- It depends on the nature of the gas.
- Low temperatures favor physisorption.

3. **Analyzing the Options**:
- **Increase in Temperature**: This would decrease physisorption because higher temperatures provide more kinetic energy to gas molecules, which makes them less likely to adhere to the surface.
- **Decrease in Temperature**: Lower temperatures favor physisorption as the kinetic energy of gas molecules decreases, allowing them to be more easily attracted to the surface.
- **Decrease in Surface Area**: A decrease in surface area would reduce the extent of physisorption, as there would be less surface for the gas molecules to adhere to.
- **Decrease in the Strength of Van der Waals Forces**: This would also decrease physisorption, as weaker forces would result in less attraction between the gas and the surface.

4. **Conclusion**:
- From the analysis, the option that correctly states the relationship is **decrease in temperature**. Therefore, the extent of physisorption of a gas increases with a decrease in temperature.

### Final Answer:
The extent of physisorption of a gas increases with **decrease in temperature**.

---