Sublimation is a physical change. It involves the transition of a substance directly from the solid phase to the gas phase without passing through the intermediate liquid phase. This process is purely a change in the state of matter and does not alter the chemical composition of the substance.
For example, when dry ice (solid carbon dioxide) sublimates, it turns directly into carbon dioxide gas. The molecules of carbon dioxide remain the same; only their physical state changes. This is why sublimation is considered a physical change rather than a chemical change.