Which characteristic is not correct for physical adsorption? 

Options

A. Adsorption is spontaneous
B. both enthalpy and entropy change of adsorption are negative
C. Adsorption on solid is reversible
D. Adsorption increases with increase in temperature

Answer

To determine which characteristic is not correct for physical adsorption, we will analyze the given statements one by one.

### Step-by-Step Solution:

1. **Understanding Physical Adsorption**:
Physical adsorption, also known as physisorption, is a type of adsorption that involves weak van der Waals forces. It is generally characterized by lower energy changes compared to chemical adsorption.

2. **Analyzing the Statements**:
- **Statement 1**: "Adsorption is spontaneous."
- This statement is generally true for physical adsorption. It occurs spontaneously under appropriate conditions.

- **Statement 2**: "Both enthalpy and entropy change of adsorption are negative."
- This statement is not correct. In physical adsorption, the enthalpy change (ΔH) is negative (exothermic), but the entropy change (ΔS) is typically positive because the gaseous molecules become more ordered when they are adsorbed onto a surface.

- **Statement 3**: "Adsorption on solid is reversible."
- This statement is true. Physical adsorption is reversible, meaning that the adsorbed molecules can be desorbed easily.

- **Statement 4**: "Adsorption increases with an increase in temperature."
- This statement is incorrect. For physical adsorption, as temperature increases, the kinetic energy of the molecules increases, leading to desorption. Therefore, physical adsorption generally decreases with an increase in temperature.

3. **Conclusion**:
The characteristic that is not correct for physical adsorption is: **"Adsorption increases with an increase in temperature."**

### Final Answer:
The incorrect characteristic for physical adsorption is: **"Adsorption increases with increase in temperature."**