Condensation is the change of state from a gas to a liquid. Which choice correctly defines this process?

• A. Vaporisation is the change of a liquid to a solid
• B. Condensation is the change of a gas to a liquid
• C. Vaporisation is the cooling of a liquid
• D. Condensation is the change of a solid to a gas

Answer: (B)

Condensation is when a gas loses enough energy to become a liquid; as the gas cools (or is compressed), its molecules slow down and are drawn together into a liquid, releasing energy in the process. This exactly matches the idea of a gas turning into a liquid. The other statements describe different changes: vaporisation is liquid to gas, not gas to liquid; cooling a liquid is not describing a change of state; and a solid turning directly into a gas is sublimation, not condensation.