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Iodine, a steel-gray solid, readily vaporizes when heated. The vapor is violet in colour. If the vapor is allowed to cool, it passes directly back into the solid state. This process of passing from the solid state to the vapor state and then back to the solid state without the formation of a liquid is called sublimation. If a saturated solution of potassium nitrate is heated and then allowed to cool, crystals of the substance form on the bottom of the vessel. These are formed by precipitation, which takes place during the cooling process.
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Iodine readily vaporizes …