Which of the following statements is incorrect regarding physiosorptions ?

Options

A. More easily liquefiable gases are adsorbed readily .
B. Under high pressure it results into multi molecular layer on absorbent surface.
C. Enthalpy of adsorption `[DeltaH_("adsorption")]` is low and positive
D. It occurs because of van der Waal's forces.

Answer

To solve the question regarding which statement is incorrect about physiosorption, we can analyze each option step by step.

### Step 1: Understand Physiosorption
Physiosorption, also known as physical adsorption, is a process where molecules adhere to a surface through weak intermolecular forces, primarily Van der Waals forces. This type of adsorption does not involve significant changes in the electronic structure of the adsorbate.

### Step 2: Evaluate Each Statement

1. **Statement 1**: "More easily liquefiable gases are adsorbed readily."
- **Analysis**: This statement is correct. Easily liquefiable gases have stronger intermolecular forces and can be adsorbed more readily due to their ability to interact effectively with the surface of the adsorbent.

2. **Statement 2**: "Under high pressure, it results in multi-molecular layers on adsorbent surface."
- **Analysis**: This statement is also correct. At high pressures, multiple layers of adsorbate can form on the adsorbent surface, which is characteristic of physiosorption.

3. **Statement 3**: "Enthalpy of adsorption is low and positive."
- **Analysis**: This statement is incorrect. The enthalpy of adsorption for physiosorption is typically low and negative, indicating that the process is exothermic. The values usually range from -20 to -40 kJ/mol.

4. **Statement 4**: "It occurs because of Van der Waals forces."
- **Analysis**: This statement is correct. Physiosorption occurs due to weak Van der Waals forces, which are the primary interactions involved in this type of adsorption.

### Conclusion
Based on the analysis, the incorrect statement regarding physiosorption is **Statement 3**, which claims that the enthalpy of adsorption is low and positive.

### Final Answer
**The incorrect statement regarding physiosorption is: "Enthalpy of adsorption is low and positive."**

---