Which statement is not correct 

Options

A. Physical adsorption is due to vander Waals'forces
B. Physical adsorption decreases at high temperature and low pressure
C. Physical adsorption is reversible
D. Adsorption energy for a chemical adsorp tion is generally lesser than that of physical adsorption

Answer

To determine which statement is not correct regarding adsorption, let's analyze each statement step by step.

### Step 1: Analyze the Statements
1. **Statement 1**: Physical adsorption is due to van der Waals forces.
- **Analysis**: This statement is correct. Physical adsorption (physisorption) occurs due to weak van der Waals forces between the adsorbate and the adsorbent.

2. **Statement 2**: Physical adsorption decreases at high temperature and low pressure.
- **Analysis**: This statement is also correct. Physical adsorption is favored at low temperatures and high pressures. As temperature increases, the kinetic energy of the molecules increases, which can lead to desorption.

3. **Statement 3**: Physical adsorption is reversible.
- **Analysis**: This statement is correct as well. Physical adsorption is generally reversible, meaning that the adsorbate can be removed from the adsorbent without significant changes to the adsorbent.

4. **Statement 4**: Adsorption energy for chemical adsorption is generally lesser than that of physical adsorption.
- **Analysis**: This statement is incorrect. Chemical adsorption (chemisorption) involves the formation of chemical bonds, which typically have higher energy compared to the van der Waals forces involved in physical adsorption. Therefore, the adsorption energy for chemical adsorption is generally greater than that of physical adsorption.

### Conclusion
The statement that is not correct is **Statement 4**: "Adsorption energy for chemical adsorption is generally lesser than that of physical adsorption."

### Final Answer
The incorrect statement is: "Adsorption energy for chemical adsorption is generally lesser than that of physical adsorption."

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