Which term describes the process whereby a substance converts directly from a solid to a gas?

The term that describes the process of a substance converting directly from a solid to a gas is sublimation. This phenomenon occurs under specific conditions of temperature and pressure, allowing the solid to bypass the liquid state entirely and transition directly to a gaseous form. A common example of sublimation is the transformation of dry ice (solid carbon dioxide) directly into carbon dioxide gas without becoming a liquid first.

In contrast, melting refers to the process where a solid becomes a liquid, which is not applicable here as the question involves a transition to a gas. Condensation is the process by which a gas turns into a liquid, again unrelated to the direct conversion of a solid to gas. Deposition is the reverse of sublimation, where a gas transitions directly into a solid without passing through the liquid phase, thus further clarifying the unique nature of sublimation.