The term 'liquefying' as used in the material most closely describes which action?

• A. Cooling a gaseous oxygen to cryogenic temperatures
• B. Compressing oxygen and placing in tank to reach a high psi
• C. Splitting water into hydrogen and oxygen
• D. Storing oxygen in a cryogenic Dewar vessel

Answer: (B)

Liquefying a gas means turning it into a liquid by removing energy from the gas, typically by cooling it to very low (cryogenic) temperatures until it condenses into a liquid.

Cooling a gaseous oxygen to cryogenic temperatures directly achieves this condensation, producing liquid oxygen. Storing oxygen in a cryogenic Dewar vessel is about holding that already-liquefied oxygen, not turning it into liquid. Splitting water into hydrogen and oxygen is electrolysis, a chemical process that creates gases from a liquid, not liquefying an existing gas. Compressing oxygen to a high pressure in a tank densifies the gas but does not turn it into a liquid.

So the action that matches liquefying most closely is cooling the gas to cryogenic temperatures to condense it into a liquid.