which of the following statement is not correct ?

Options

A. physical adsorption is due to van der Waals' forces
B. physical adsorption is irreversible
C. Chemical adsorption increases with increase in temperature upto certain limit than decreases
D. Enthaply of adsorption `(//DeltaH//)` of a chemical is greater than of physical adsorption

Answer

To determine which statement is not correct, we will analyze each option one by one.

### Step-by-Step Solution:

1. **Option 1: Physical adsorption is due to Van der Waals forces.**
- **Analysis:** Physical adsorption, also known as physisorption, occurs due to weak Van der Waals forces between the adsorbate and the adsorbent. This statement is correct.

2. **Option 2: Physical adsorption is irreversible.**
- **Analysis:** Physical adsorption is generally reversible. The adsorbate can be removed from the surface without significant energy input. This statement is incorrect.

3. **Option 3: Chemical adsorption increases with increases in temperature up to a certain limit, then decreases.**
- **Analysis:** Chemical adsorption (chemisorption) typically requires activation energy, and its rate can increase with temperature up to a certain point, after which it may decrease due to desorption or other factors. This statement is correct.

4. **Option 4: Enthalpy of adsorption of chemical adsorption is greater than that of physical adsorption.**
- **Analysis:** The enthalpy of adsorption for chemical adsorption is indeed greater than that for physical adsorption because chemical bonds are stronger than Van der Waals forces. This statement is correct.

### Conclusion:
The statement that is not correct is **Option 2: Physical adsorption is irreversible.**