Which forms multi molecular layers during adsorption :

Options

A. Physical adsorption always increases when
temperature increases
B. van der Waals' adsorption
C. Chemical adsorption is reversible
D. All of these

Answer

**Step-by-Step Solution:**

1. **Understanding Adsorption:**
- Adsorption is the process where atoms, ions, or molecules from a gas, liquid, or dissolved solid adhere to a surface. This creates a film of the adsorbate on the surface of the adsorbent.

2. **Types of Adsorption:**
- There are two main types of adsorption:
- **Physisorption (Physical Adsorption):** This involves weak Van der Waals forces and does not involve any significant energy change. It is generally reversible.
- **Chemisorption (Chemical Adsorption):** This involves the formation of a chemical bond between the adsorbate and the adsorbent, which is usually stronger and often irreversible.

3. **Multi-molecular Layers:**
- Multi-molecular layers refer to the formation of more than one layer of adsorbate molecules on the surface of the adsorbent. This typically occurs when the adsorbate can adhere to itself as well as to the surface.

4. **Physisorption and Multi-molecular Layers:**
- Physisorption allows for the formation of multi-molecular layers because the weak Van der Waals forces enable gas molecules to be adsorbed one over the other.
- Under conditions of high pressure, more gas molecules can be forced onto the surface, leading to the formation of multiple layers.

5. **Conclusion:**
- Therefore, the type of adsorption that forms multi-molecular layers is **Physisorption**.

**Final Answer:**
Physisorption forms multi-molecular layers during adsorption.

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