Final answer:
Sublimation is the process by which a gas changes directly to a solid, bypassing the liquid phase.
Step-by-step explanation:
Sublimation is the process by which a gas changes directly to a solid. It bypasses the liquid phase. For example, at room temperature and standard pressure, dry ice (solid CO₂) sublimes, appearing to gradually disappear without ever forming any liquid. Snow and ice also undergo sublimation at temperatures below the melting point of water.
The reverse process of sublimation is called deposition. Deposition is the process in which gaseous substances condense directly into the solid state, bypassing the liquid state. The formation of frost is an example of deposition.