Select correct statements:

Options

A. A real gas can be liquified at critical temperature
B. Critical pressure is the maximum pressure at which a substance is present in its liquid state at `T_(C)`
C. Ideal gas can be liquified below `T_(C)`
D. Critical volume is the molar volume of substance in gaseous state at `T_(C)` and `P_(C)`

Explanation

To solve the question of selecting the correct statements regarding the gaseous state, we will analyze each statement one by one based on the information provided in the video transcript.

### Step-by-step Solution:

1. **Statement 1: A real gas can be liquefied at critical temperature.**
- **Analysis:** This statement is false. Not all real gases can be liquefied at the critical temperature. The critical temperature (Tc) is the temperature above which a gas cannot be liquefied, regardless of the pressure applied. Therefore, this statement is incorrect.

2. **Statement 2: Critical pressure is the maximum pressure at which a substance is present in its liquid state at Tc.**
- **Analysis:** This statement is also false. Critical pressure (Pc) is the pressure required to liquefy a gas at its critical temperature. However, at the critical point, the distinction between liquid and gas disappears, meaning the substance does not exist purely in the liquid state. Hence, this statement is incorrect.

3. **Statement 3: A real gas can be liquefied below the Tc.**
- **Analysis:** This statement is true. Real gases can indeed be liquefied when they are below their critical temperature (Tc) by applying sufficient pressure. This is a fundamental property of real gases, making this statement correct.

4. **Statement 4: Critical volume is the molar volume of a substance in the gaseous state at Tc and Pc.**
- **Analysis:** This statement is false. At the critical point (Tc and Pc), the distinction between the gaseous state and liquid state disappears, meaning that we cannot define a specific molar volume for the gaseous state at this point. Therefore, this statement is incorrect.

### Summary of Correct Statements:
- The only correct statement is: **A real gas can be liquefied below the Tc.**