The statement that is NOT correct is :

Options

A. compressibility factor measures the deviation of real gas from ideal behaviour
B. van der Waals' constant 'a' measures extent of intermolecular attractive forces for real gases
C. critical temperature is the lowest temperature at which liquification of a gas first occurs
D. Boyle point depends on the nature of the real gas.

Explanation

To solve the question regarding which statement is NOT correct, we will analyze each statement one by one.

### Step 1: Analyze the first statement
**Statement 1:** "The compressibility factor measures the deviation of real gas from the ideal gas behavior."

- **Explanation:** The compressibility factor (Z) is defined as Z = PV/nRT. For an ideal gas, Z = 1. If Z ≠ 1, it indicates that the gas deviates from ideal behavior. Thus, this statement is correct.

### Step 2: Analyze the second statement
**Statement 2:** "The Van der Waals constant A measures the extent of intermolecular attractive force of real gas."

- **Explanation:** In the Van der Waals equation, the constant A accounts for the attractive forces between gas molecules. Therefore, this statement is also correct.

### Step 3: Analyze the third statement
**Statement 3:** "The critical temperature (TC) is the lowest temperature at which liquefaction of gas first occurred."

- **Explanation:** This statement is incorrect. The critical temperature is actually the highest temperature at which a gas can be liquefied. Above this temperature, no amount of pressure can cause the gas to liquefy. Therefore, this statement is NOT correct.

### Step 4: Analyze the fourth statement
**Statement 4:** "The boiling point depends on the nature of the real gas."

- **Explanation:** This statement is true. The boiling point of a substance is influenced by its molecular structure and intermolecular forces. Thus, this statement is correct.

### Conclusion
The statement that is NOT correct is the third statement regarding critical temperature.

### Summary of the Steps:
1. **First Statement:** Correct (compressibility factor measures deviation).
2. **Second Statement:** Correct (Van der Waals constant A measures attractive forces).
3. **Third Statement:** Incorrect (critical temperature is the highest temperature for liquefaction).
4. **Fourth Statement:** Correct (boiling point depends on the nature of the gas).

### Final Answer:
The statement that is NOT correct is the third statement.

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