Question

A gas can be liquified by pressure alone only, when its temperature is ___________ its critical temperature.

• A. more than
• B. less than
• C. less than or equal to
• D. equal to or higher than

Answer 1

The correct option is C less than or equal to

Critical temperature of a substance is the temperature at and above which vapor of the substance cannot be liquefied, no matter how much pressure is applied.

Critical pressure of a substance is the pressure required to liquefy a gas at its critical temperature.

Therefore, it can be liquefied only when temp is less than or equal to its critical temperature.

Hence, option C is correct.