An ideal gas obeying theory of gases can be liquefied if

Options

A. Its temperature is more than critical temperature `T_(c)`
B. Its pressure is more than critical pressure `P_(c)`
C. Its pressure is less than at a temperature less than
D. It cannot be liquefied at any value of P and T

Explanation

To determine under what conditions an ideal gas can be liquefied, we need to analyze the properties of ideal gases and the concept of intermolecular forces.

### Step-by-Step Solution:

1. **Understanding Ideal Gases**:
- Ideal gases are theoretical gases that perfectly follow the ideal gas law (PV=nRT). They are characterized by the absence of intermolecular forces of attraction between their molecules.

2. **Intermolecular Forces**:
- For a gas to be liquefied, the molecules must come close enough together for intermolecular forces to act. In ideal gases, these forces are negligible or considered absent.

3. **Conditions for Liquefaction**:
- Liquefaction occurs when gas molecules are brought close enough together that attractive forces can overcome the kinetic energy of the molecules. This typically requires high pressure and low temperature in real gases.

4. **Critical Temperature and Pressure**:
- Critical temperature (Tc) is the temperature above which a gas cannot be liquefied, regardless of the pressure applied. Critical pressure (Pc) is the pressure required to liquefy a gas at its critical temperature.
- These concepts apply to real gases, which do have intermolecular forces.

5. **Conclusion for Ideal Gases**:
- Since ideal gases have no intermolecular forces, they cannot be liquefied under any conditions of temperature or pressure. Therefore, an ideal gas cannot be liquefied.

6. **Final Answer**:
- An ideal gas cannot be liquefied at any value of pressure and temperature.