Which is/are correct statements?

Options

A. Physical adsorption always increases when
temperature increases
B. Physical adsorption decreases when
temperature increases
C. Chemical adsorption is reversible
D. Monolayer is formed is chemical adsorption

Answer

To determine which statements are correct regarding physical and chemical adsorption, let's analyze each option step by step.

### Step-by-Step Solution:

1. **Statement A: Physical adsorption always increases when temperature increases.**
- **Analysis:** Physical adsorption involves weak Van der Waals forces. When the temperature increases, the kinetic energy of the molecules also increases. This increased energy can lead to the breaking of these weak bonds. Therefore, physical adsorption actually decreases with an increase in temperature.
- **Conclusion:** This statement is **incorrect**.

2. **Statement B: Physical adsorption decreases when temperature increases.**
- **Analysis:** As established in the analysis of Statement A, the increase in temperature leads to an increase in kinetic energy, which weakens the Van der Waals forces responsible for physical adsorption. Hence, physical adsorption decreases with an increase in temperature.
- **Conclusion:** This statement is **correct**.

3. **Statement C: Chemical adsorption is reversible.**
- **Analysis:** Chemical adsorption involves the formation of strong covalent or ionic bonds. These bonds are not easily broken and thus chemical adsorption is generally considered irreversible. In contrast, physical adsorption is reversible due to the weak nature of the bonds involved.
- **Conclusion:** This statement is **incorrect**.

4. **Statement D: Monolayer is formed in chemical adsorption.**
- **Analysis:** In chemical adsorption, strong covalent or ionic bonds are formed, and typically only a single layer (monolayer) of adsorbate is formed on the adsorbent surface. This is because once the strong bond is formed, there is no further adsorption of additional layers.
- **Conclusion:** This statement is **correct**.

### Final Summary:
- **Correct Statements:** B and D
- **Incorrect Statements:** A and C