Physical Properties

Radon is a colorless, odorless gas with a density of 9.72 grams per liter, making it seven times dense as air. It is the densest gas known. Radon dissolves in water and becomes a clear, colorless liquid below its boiling point. At even lower temperature, liquid radon freezes. As a solid, it's color changes from yellow to orangish-red as the temperature is lowered even further.