Physical adsorption is appreciable at

Options

A. Higher temperature
B. Lower temperature
C. At room temperature
D. `100^@C`

Answer

To solve the question regarding the conditions under which physical adsorption is appreciable, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Physical Adsorption**:
- Physical adsorption, also known as physisorption, involves weak van der Waals forces between the adsorbate (the substance being adsorbed) and the adsorbent (the surface on which adsorption occurs).

2. **Temperature Dependence**:
- Physical adsorption is generally favored at lower temperatures. This is because lower temperatures increase the stability of the adsorbed state due to reduced kinetic energy of the molecules, allowing them to adhere more effectively to the surface.

3. **Effect of Pressure**:
- The extent of physical adsorption increases with an increase in gas pressure. At lower temperatures, the molecules have less energy to escape back into the gas phase, thus enhancing adsorption.

4. **Exothermic Nature**:
- Physical adsorption is an exothermic process, meaning it releases heat. According to Le Chatelier's principle, if the temperature increases, the equilibrium will shift to favor the reactants (the gas phase), thus decreasing the extent of adsorption.

5. **Evaluating the Options**:
- **High Temperature**: Incorrect, as physical adsorption decreases with increasing temperature.
- **Lower Temperature**: Correct, as physical adsorption is appreciable at lower temperatures.
- **Room Temperature**: Incorrect, as it is not as favorable as lower temperatures.
- **100 Degrees Celsius**: Incorrect, as this is a high temperature which would reduce physical adsorption.

6. **Conclusion**:
- The correct answer is that physical adsorption is appreciable at lower temperatures.

### Final Answer:
Physical adsorption is appreciable at **lower temperatures**.

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