When a compressed gas is allowed to expand through a porous plug at temperature above its inversion temperature, there is

Options

A. a fall in temperature
B. a rise in temperature
C. neither a fall nor a rise in temperature
D. a fall in temperature first, followed by a rise in temperature.

Answer

### Step-by-Step Solution:

1. **Understanding the Scenario**: The question involves a compressed gas that is allowed to expand through a porous plug at a temperature above its inversion temperature.

2. **Defining Inversion Temperature**: The inversion temperature (T_i) is the temperature above which a gas, when allowed to expand, exhibits heating effects rather than cooling effects.

3. **Joule-Thomson Effect**: When a gas expands through a porous plug, it can either cool down or heat up depending on its initial temperature relative to the inversion temperature. If the temperature is above the inversion temperature, the gas will experience a heating effect during expansion.

4. **Analyzing the Given Options**:
- **Option 1**: A fall in temperature - This is incorrect because at temperatures above the inversion temperature, the gas heats up.
- **Option 2**: A rise in temperature - This is correct as the gas heats up during expansion above the inversion temperature.
- **Option 3**: Neither a fall nor a rise in temperature - This is incorrect since there is a clear rise in temperature.
- **Option 4**: A fall in temperature first, followed by a rise in temperature - This is also incorrect because there is no initial fall in temperature when expanding above the inversion temperature.

5. **Conclusion**: The correct answer is **Option 2: A rise in temperature**.