Answer: Above which a gas cannot be liquefied by pressure alone.
- A Below which a substance cannot exist in the gaseous state at all
- B Above which a gas cannot be liquefied by pressure alone
- C At which a gas spontaneously condenses regardless of the applied pressure
- D At which the vapour pressure of the substance drops to exactly zero
Correct answer: B. Above which a gas cannot be liquefied by pressure alone
Explanation: Above the critical temperature, no amount of pressure can liquefy a gas.
Boyle's law: at constant temperature the pressure of a fixed mass of gas is inversely proportional to its volume (P ∝ 1/V), so the P–V plot is a hyperbola — halving the volume doubles the pressure. Image: Reginaprice2013, CC BY-SA 3.0, via Wikimedia Commons.
Concept context
Discover why gases expand to fill any container while liquids flow and solids hold their shape. Master the gas laws, the ideal gas equation, and the reasons real gases deviate from ideal behavior.