Which of the following statements about phase changes is true?

• A. Sublimation is the phase change from liquid to gas.
• B. Vaporization includes condensation.
• C. Condensation is the gas-to-liquid phase change when cooled.
• D. Freezing is the gas-to-liquid phase change.

Answer: (C)

The main idea is how matter changes between states and the direction of that change, which is dictated by energy flow. Condensation is the gas-to-liquid change that happens when a gas is cooled and loses energy, causing its particles to slow down and pack together into a liquid. Think of water vapor turning into liquid water on a cold surface or forming clouds as air cools.

Why the other descriptions don’t fit: sublimation is solid turning directly into gas, not liquid to gas. Vaporization refers to liquid turning into gas (evaporation or boiling), not gas turning into liquid. Freezing is liquid turning into solid, not gas to liquid. So condensation is the correct gas-to-liquid change when cooled.