Which of the following will favour the reversal of physical adsorption?

Options

A. Increasing the pressure of the gas and decreasing the temperature of the surface.
B. Decreasing the pressure of the gas and increasing the temperature of the surface.
C. Decreasing both, the pressure of the gas and the temperature of the surface.
D. Increasing both, the pressure of the gas and the temperature of the surface.

Answer

To determine which of the following will favor the reversal of physical adsorption, we need to understand the principles of physical adsorption, particularly its dependence on temperature and pressure.

### Step-by-Step Solution:

1. **Understanding Physical Adsorption**:
- Physical adsorption occurs when a gas (adsorbate) adheres to a solid surface (adsorbent) through weak van der Waals forces, without forming any chemical bonds.
- This process is exothermic, meaning it releases heat when it occurs.

2. **Effect of Temperature**:
- Since physical adsorption is exothermic, it is favored at lower temperatures.
- If we increase the temperature, the kinetic energy of the molecules increases, which can lead to a decrease in the extent of adsorption. Thus, increasing temperature will favor the reversal of physical adsorption.

3. **Effect of Pressure**:
- Increasing the pressure of the gas increases the extent of physical adsorption because the gas molecules are forced closer to the solid surface.
- Conversely, decreasing the pressure will favor the reversal of physical adsorption as it reduces the number of gas molecules available to adhere to the surface.

4. **Analyzing the Options**:
- **Option 1**: Increasing the pressure of the gases and decreasing the temperature of the surfaces.
- Increasing pressure will increase adsorption, so this option does not favor reversal.
- **Option 2**: Decreasing the pressure of the gas and increasing the temperature of the surface.
- Decreasing pressure will decrease adsorption, and increasing temperature will also decrease adsorption. This option favors reversal.
- **Option 3**: Decreasing both the pressure of the gas and the temperature of the surface.
- Decreasing pressure decreases adsorption, but decreasing temperature increases adsorption. This option does not favor reversal.
- **Option 4**: Increasing both the pressure of the gas and the temperature of the surface.
- Increasing pressure increases adsorption, and increasing temperature decreases adsorption. This option does not favor reversal.

5. **Conclusion**:
- The only option that favors the reversal of physical adsorption is **Option 2**: Decreasing the pressure of the gas and increasing the temperature of the surface.

### Final Answer:
**Option 2: Decreasing the pressure of the gas and increasing the temperature of the surface.**

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