What process involves the conversion of solid directly into gas?

The correct choice is sublimation, which is the process where a solid material transitions directly into a gas without passing through the liquid state. This occurs under specific conditions of pressure and temperature. A common example of sublimation is dry ice (solid carbon dioxide) which, when exposed to atmospheric pressures, turns directly into carbon dioxide gas. This transition occurs because the molecules of the solid gain enough energy to overcome intermolecular forces and escape into the gas phase.

In this context, condensation refers to the transformation of gas into a liquid, and evaporation is the process where a liquid turns into a gas. Deposition is the opposite of sublimation; it is the process where gas transitions directly into a solid. These distinctions highlight why sublimation is specifically related to the direct conversion from solid to gas.