The purification method based on the following physical transformation is: ( X ) Solid → Heat ( X ) Vapour → Cool ( X ) Solid

The purification method based on the following physical transformation is : $$\underset{(\mathrm{X})}{\text { Solid }} \xrightarrow{\text { Heat }} \underset{(\mathrm{X})}{\text { Vapour }} \xrightarrow{\text { Cool }} \underset{(\mathrm{X})}{\text { Solid }} $$