Which of the following properties are related to physical adsorption ?

Options

A. Reversible
B. Formation of unimolecular layer
C. Low heat of adsorption
D. Occurs at high temperature

Answer

To determine which properties are related to physical adsorption, we will analyze each option based on the characteristics of physical adsorption.

### Step-by-Step Solution:

1. **Understanding Physical Adsorption**:
- Physical adsorption, also known as physisorption, occurs when gas molecules (adsorbates) adhere to a solid surface (adsorbent) through weak intermolecular forces, specifically Van der Waals forces. This process is generally reversible.

2. **Analyzing the Options**:
- **Option 1: Reversible**
- Physical adsorption is indeed reversible. The adsorbate can be removed from the adsorbent by increasing the temperature or decreasing the pressure.
- **Conclusion**: This option is correct.

- **Option 2: Formation of unimolecular layer**
- In physical adsorption, multiple layers of adsorbate can form on the adsorbent surface, not just a single unimolecular layer. Therefore, this statement is incorrect.
- **Conclusion**: This option is incorrect.

- **Option 3: Low heat of adsorption**
- The heat of adsorption for physical adsorption is relatively low, typically in the range of 20 to 40 kJ/mol. This is characteristic of physisorption.
- **Conclusion**: This option is correct.

- **Option 4: Occurs at high temperature**
- Physical adsorption occurs at low temperatures. As temperature increases, the adsorption process tends to decrease. Therefore, this statement is incorrect.
- **Conclusion**: This option is incorrect.

3. **Final Assessment**:
- Based on the analysis, the properties related to physical adsorption are:
- Option 1: Reversible (Correct)
- Option 3: Low heat of adsorption (Correct)

### Summary of Correct Options:
- The properties related to physical adsorption are:
- Reversible
- Low heat of adsorption