At high pressure, the entire surface gets covered by a monomolecular layer of the gas follows

Options

A. three-halved order
B. second-order
C. first-order
D. zero-order

Answer

To solve the question regarding the order of adsorption when the entire surface gets covered by a monomolecular layer of gas at high pressure, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Concept of Adsorption**:
- Adsorption is the process where gas molecules adhere to the surface of a solid. In this case, we are dealing with a monomolecular layer of gas on a solid surface.

2. **Identifying the Conditions**:
- The question specifies that this adsorption occurs at high pressure. At high pressure, the gas molecules are forced closer to the surface, leading to a greater likelihood of adsorption.

3. **Recognizing the Type of Adsorption**:
- The formation of a monomolecular layer indicates that the adsorption is likely physisorption, which is a physical process involving weak van der Waals forces.

4. **Analyzing the Freundlich Isotherm**:
- The Freundlich isotherm describes how the amount of gas adsorbed varies with pressure. At low pressures, the adsorption increases linearly with pressure, indicating first-order kinetics.
- However, at high pressures, the adsorption reaches a saturation point where the surface is fully covered, and further increases in pressure do not lead to an increase in adsorption.

5. **Determining the Order of Reaction**:
- At high pressure, since the adsorption does not change with an increase in pressure (the graph becomes constant), it indicates that the rate of adsorption is independent of the pressure.
- This behavior corresponds to zero-order kinetics, where the rate of reaction is constant and does not depend on the concentration of the reactants.

6. **Conclusion**:
- Therefore, at high pressure, the adsorption of gas onto the surface follows zero-order kinetics.

### Final Answer:
At high pressure, the entire surface gets covered by a monomolecular layer of the gas follows **zero-order kinetics**.

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