Only the surface atoms in an adsorbent play an active role in adsorption. These atoms possess some residual force such as van der Waals forces and chemical forces. In the process of adsorption. Weak adsorbate is substituting by strong adsorbete. Activated charcoal used in the gas mask is already exposed to the atmospheric air, so gases and water vapours in air are adsorbed on its surface. When the mask is exposed to chlorine atmosphere, the gases are displaced by chlorine. In general, easily liquefiable gases such as `CO_(2),NH_(3),Cl_(2),` and `SO_(2)` are adsorbed to a greater extent than the elemental gases, e.g., `H_(2),N_(2),O_(2),` He, etc.
Gas mask works on the principle of

Options

A. Chemical adsorption
B. Physical adsorption
C. Both physical adsorption and chemical adsorption
D. None of these

Answer

To solve the question regarding the principle on which gas masks operate, we need to analyze the concepts of adsorption and the specific characteristics of the gases involved.

### Step-by-Step Solution:

1. **Understanding Adsorption**:
- Adsorption is the process by which atoms, ions, or molecules from a gas, liquid, or dissolved solid adhere to a surface. It can occur through two main types: physical adsorption (physisorption) and chemical adsorption (chemisorption).

2. **Physical Adsorption (Physisorption)**:
- In physisorption, the forces involved are weak van der Waals forces. This type of adsorption is generally reversible and occurs at lower temperatures. It is characterized by the fact that the adsorbate does not undergo any significant chemical change.

3. **Chemical Adsorption (Chemisorption)**:
- In chemisorption, the forces involved are much stronger and involve the formation of chemical bonds between the adsorbate and the adsorbent. This process is usually irreversible and involves a significant energy change.

4. **Gas Mask Functionality**:
- Activated charcoal in gas masks is designed to adsorb harmful gases and vapors from the air. When the mask is exposed to atmospheric air, various gases, including water vapor, are adsorbed onto the surface of the charcoal.

5. **Behavior of Gases**:
- The question mentions that easily liquefiable gases like CO₂, NH₃, Cl₂, and SO₂ are adsorbed to a greater extent than elemental gases such as H₂, N₂, and O₂. This indicates that both physical and chemical adsorption processes are at play, as the activated charcoal can effectively capture a variety of gas types.

6. **Conclusion**:
- Since the gas mask utilizes activated charcoal to adsorb gases through both weak van der Waals forces (physical adsorption) and stronger chemical bonds (chemical adsorption), it operates on the principle of **both physical and chemical adsorption**.

### Final Answer:
The gas mask works on the principle of **both physical adsorption and chemical adsorption** (Option C).