The process described as liquefying involves which action?

• A. Compress the oxygen, then put it in compressed tank, continue to do so until they get 2250 psi per square inch
• B. Cooling atmospheric air until it becomes liquid
• C. Splitting water into hydrogen and oxygen
• D. Mixing oxygen with acetylene to form a compound

Answer: (A)

Liquefying a gas means turning it into a liquid by removing heat. In practice, gases like oxygen must be cooled to very low temperatures—below their condensation point—so their molecules move slow enough to form a liquid. Merely increasing pressure won’t reliably liquefy a gas at room temperature; the gas would simply become pressurized but stay a gas unless it’s cooled to the right temperature or kept in cryogenic conditions. So the action described as liquefying is cooling the gas until it becomes a liquid. The other options describe compression to high pressure, splitting water, or mixing gases, none of which capture the actual process of turning a gas into a liquid.