Deposition is a gas turning directly into a solid; frost forms on a cold surface. This is known as which process?

• A. Sublimation.
• B. Condensation.
• C. Deposition.
• D. Evaporation.

Answer: (C)

Deposition is the process where a gas changes directly into a solid, skipping the liquid phase. Frost forms on a cold surface because water vapor in the air loses enough energy when it meets the frigid surface to crystallize straight into solid ice, rather than first becoming liquid water. This direct gas-to-solid change is what makes frost appear as a solid coating. For comparison, condensation is gas to liquid, sublimation is solid to gas, and evaporation is liquid to gas, so they describe different pathways between phases.