Which of the following statements is true in the case of physical adsorption of gases on solids 

Options

A. it is exothermic process
B. it depends on the ease of liquification of the gas
C. it decreases with increase in temperature
D. all the above

Answer

To determine which statements are true regarding the physical adsorption of gases on solids, we will analyze each statement step by step.

### Step-by-Step Solution:

1. **Understanding Physical Adsorption**:
- Physical adsorption, also known as physisorption, involves the adhesion of gas molecules onto a solid surface through weak van der Waals forces. This process is generally reversible and does not involve any significant changes in the electronic structure of the adsorbate or adsorbent.

2. **Analyzing the Statements**:
- **Statement 1**: "It is an exothermic process."
- This statement is true. Physical adsorption releases energy when gas molecules adhere to the surface, making it an exothermic process. The change in enthalpy (ΔH) is negative.

- **Statement 2**: "It depends on the ease of liquefaction of the gas."
- This statement is also true. Gases that are easily liquefiable tend to have stronger van der Waals forces, which enhances their ability to be adsorbed. Therefore, the ease of liquefaction is a significant factor in physical adsorption.

- **Statement 3**: "It decreases with increase in temperature."
- This statement is true as well. Since physical adsorption is an exothermic process, increasing the temperature typically leads to a decrease in the extent of adsorption. Higher temperatures provide more kinetic energy to the gas molecules, which can overcome the weak van der Waals forces holding them to the surface.

3. **Conclusion**:
- All three statements regarding physical adsorption are correct. Therefore, the correct answer is that all of the above statements are true.

### Final Answer:
All of the above statements regarding physical adsorption of gases on solids are true.

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