Read the following statements and identify the incorrect statement .

Options

A. Volume of one mole of a gas at critical temperature is called molar volume .
B. Pressure of a gas at critical temperature is called critical pressure .
C. The critical temperature , pressure and volume are called critical constants .
D. Critical temperature is the highest temperature at which a gas can exist as liquid , above this temperature it is a gas .

Explanation

To solve the question, we need to analyze the statements provided and identify which one is incorrect. Here’s a step-by-step breakdown of the solution:

### Step 1: Understand the Statements
We have four statements to evaluate. We will go through them one by one.

### Step 2: Evaluate Statement A
- **Statement A**: "Volume of one mole of gas at critical temperature is called molar volume."
- **Analysis**: This statement is incorrect. The correct term for the volume of one mole of gas at critical temperature is "critical volume," not "molar volume." Molar volume refers to the volume occupied by one mole of a substance at a specified temperature and pressure.

### Step 3: Evaluate Statement B
- **Statement B**: "Pressure of a gas at critical temperature is called as critical pressure."
- **Analysis**: This statement is correct. The pressure at which a gas can exist in equilibrium with its liquid phase at the critical temperature is indeed referred to as critical pressure.

### Step 4: Evaluate Statement C
- **Statement C**: "The critical temperature, pressure, and volume are called critical constants."
- **Analysis**: This statement is also correct. The critical temperature, critical pressure, and critical volume are collectively known as critical constants.

### Step 5: Evaluate Statement D
- **Statement D**: "Critical temperature is the highest temperature at which a gas can exist as liquid and above this temperature it is a gas."
- **Analysis**: This statement is correct. The critical temperature is indeed the maximum temperature at which a substance can exist as a liquid; above this temperature, it cannot condense into a liquid, regardless of pressure.

### Conclusion
After evaluating all the statements, we find that:
- Statement A is incorrect.
- Statements B, C, and D are correct.

Thus, the answer to the question is:
**Option A** is the incorrect statement.

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