Critical temperature concept check: “The temperature below which a gas is always liquefied is known as the critical temperature.” Evaluate the statement.

Introduction / Context:
Critical temperature (T_c) is a fundamental thermodynamic property on phase diagrams. Misunderstanding its definition leads to errors in liquefaction and refrigeration applications.

Given Data / Assumptions:

• No specific gas; general definition is required.
• Standard thermodynamic definitions apply.

Concept / Approach:
The correct definition is: the critical temperature is the temperature above which a substance cannot be liquefied by pressure alone. Below T_c, the gas can be liquefied if sufficient pressure is applied; at or above T_c, no amount of pressure yields a separate liquid phase.

Step-by-Step Solution:

Verification / Alternative check:
Phase diagrams show that liquid–vapour coexistence exists only below T_c; however, attaining liquid still requires appropriate pressure conditions.

Why Other Options Are Wrong:
“Correct only for ideal gases/1 atm/below triple point” misrepresent T_c; the correct definition is universal and not limited to those conditions.

Common Pitfalls:
Assuming temperature alone guarantees condensation; both temperature and pressure determine phase state below T_c.

Final Answer:
Incorrect