What process involves a solid turning directly into a gas?

Sublimation is the process in which a solid transitions directly into a gas without passing through the liquid state. This occurs under specific conditions, often involving a decrease in pressure or an increase in temperature that provides sufficient energy for the molecules in the solid to break free from their rigid structure. A common example of sublimation is dry ice (solid carbon dioxide), which changes directly from a solid to carbon dioxide gas at atmospheric pressure.

The other processes listed involve different phases of matter. Evaporation refers to the transition of a liquid to gas, condensation is the process where gas transforms back into a liquid, and deposition involves the conversion of a gas directly into a solid, effectively the reverse of sublimation. Therefore, sublimation is uniquely defined by this direct transition from solid to gas, making it the correct choice for the question.