Which phase transition involves a solid turning into a gas?

• A. Sublimation
• B. Vaporization
• C. Condensation
• D. Melting

Answer: (A)

Sublimation is the term used to describe the phase transition in which a solid changes directly into a gas without first becoming a liquid. This process occurs under certain conditions, typically at specific temperatures and pressures, where the energy gained allows the molecules in the solid to overcome the forces holding them in place and enter the gaseous state.

For example, dry ice (solid carbon dioxide) sublimates at room temperature, transitioning directly into carbon dioxide gas, which is a practical illustration of this phenomenon. This unique transition is distinct from other phase changes like melting, which involves a solid turning into a liquid, or vaporization, which refers to a liquid turning into a gas. Condensation, on the other hand, is the process where a gas turns back into a liquid. Each of these processes involves changes in the state of matter, but sublimation specifically refers to the direct transition from solid to gas, making it the correct choice in this context.