What phase change occurs when a gas turns directly into a solid?

The phase change that occurs when a gas turns directly into a solid is known as deposition, but in the context of the choices provided, sublimation is closely related as it refers specifically to the transition from solid to gas. However, sublimation does not apply to the conversion of gas to solid.

The correct terminology for a gas transitioning directly to a solid is deposition. It happens when gas molecules lose energy and form solid particles without passing through the liquid phase. This process is commonly observed with certain substances, such as water vapor in the formation of frost on surfaces.

The options listed include terms that are associated with different phase changes, which can sometimes lead to confusion. Evaporation refers to the transition from liquid to gas, condensation is when gas turns into liquid, and freezing is the process of liquid turning into solid. Each of these choices describes other specific phase changes but does not accurately represent the gas-to-solid transition. Thus, the appropriate concept associated with gas turning directly into a solid is deposition, and while sublimation seems like a logical choice, it actually pertains to the reverse process.