Which statement is not correct ?

Options

A. Physical adsorption is due to van der Waals forces
B. Physical adsorption dereases at high temperature and low pressure
C. Physical adsorption is reversible
D. Adsorption energy for a chemical adsorption is generally lesser than that of physical adsorption

Answer

To determine which statement is not correct regarding adsorption, we will analyze each option step by step.

### Step 1: Analyze the First Statement
**Statement:** Physical adsorption is due to Van der Waals forces.

**Analysis:** This statement is correct. Physical adsorption occurs when the adsorbate molecules adhere to the surface of the adsorbent through weak Van der Waals forces.

### Step 2: Analyze the Second Statement
**Statement:** Physical adsorption decreases at high temperature and low pressure.

**Analysis:** This statement is also correct. Physical adsorption is an exothermic process, which means it is favored at lower temperatures. Additionally, increasing pressure typically increases physical adsorption, while decreasing pressure would reduce it.

### Step 3: Analyze the Third Statement
**Statement:** Physical adsorption is reversible.

**Analysis:** This statement is correct. Physical adsorption is reversible, meaning that the adsorbed molecules can be released from the surface by increasing the temperature or decreasing the pressure, leading to desorption.

### Step 4: Analyze the Fourth Statement
**Statement:** Adsorption energy for chemical adsorption is generally lesser than that of physical adsorption.

**Analysis:** This statement is incorrect. Chemical adsorption involves stronger interactions (covalent or ionic bonds) compared to physical adsorption, which is due to Van der Waals forces. Therefore, the adsorption energy for chemical adsorption is generally greater than that for physical adsorption.

### Conclusion
The statement that is not correct is the fourth one: "Adsorption energy for chemical adsorption is generally lesser than that of physical adsorption."

### Final Answer
**The incorrect statement is:** Option 4.

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