In physical adsorption, gas molecules are bound on the solid surface by

Options

A. Chemical forces
B. Electrostatic forces
C. Gravitational forces
D. Van der Waal’s forces

Answer

### Step-by-Step Text Solution:

1. **Understanding Adsorption**:
- Adsorption is the process where gas, liquid, or solid particles accumulate on the surface of a solid or liquid. This differs from absorption, where particles enter the bulk of the material.

2. **Types of Adsorption**:
- Adsorption can be categorized into two main types: physical adsorption (physisorption) and chemical adsorption (chemisorption).

3. **Physical Adsorption**:
- In physical adsorption, gas molecules are held on the surface of a solid by weak forces. These forces are not chemical bonds but rather physical interactions.

4. **Nature of the Forces**:
- The forces responsible for physical adsorption are primarily Van der Waals forces. These are weak intermolecular forces that arise from temporary dipoles in molecules.

5. **Conclusion**:
- Therefore, in physical adsorption, gas molecules are bound to the solid surface by Van der Waals forces.

### Final Answer:
In physical adsorption, gas molecules are bound on the solid surface by **Van der Waals forces**.

---