The process of a substance changing directly from solid to gas is called?

The process of a substance changing directly from solid to gas is referred to as sublimation. This phenomenon occurs without passing through the liquid phase. An example of sublimation is how dry ice (solid carbon dioxide) converts directly into carbon dioxide gas at temperatures above its sublimation point.

To further clarify, condensation is the process where a gas becomes a liquid, typically when cooling occurs. Meltation, while a term that suggests melting, is not scientifically recognized and does not describe any proper phase change that qualifies for this context. Evaporation, on the other hand, is the process of a liquid transitioning to a gas, which is distinct from the solid-to-gas transition that sublimation describes. Therefore, sublimation is the only term that accurately matches the description of a solid transforming directly into a gas.