The purification method based on the following physical transformation is:
\[
{Solid} \xrightarrow{{Heat}} {Vapour} \xrightarrow{{Cool}} {Solid}
\]
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Sublimation is a useful technique for purifying solids that can transition directly from the solid phase to the gas phase without passing through the liquid phase.
The described process involves heating a solid to produce vapor, followed by cooling the vapor back to a solid. This exemplifies sublimation, a direct solid-to-gas and then gas-to-solid phase transition, bypassing the liquid state. Sublimation is a purification technique for substances like iodine, dry ice, or camphor, which can undergo this transformation. The heat energy supplied allows molecules to overcome intermolecular forces and vaporize directly. Subsequent cooling causes the vapor to condense back into a solid, separating it from impurities. Therefore, sublimation is the appropriate purification method for the transformation detailed.
