Answer:
1) Radon is colorless at standard temperature and pressure and it is the most dense gas known. At temperature below it's freezing point is has a brilliant yellow phosphorescence. It is chemically unreactive, it is highly radioactive and has a short half life.
2) 7.5 times heavier than air and more than 100 times heavier than hydrogen. The gas liquefies at −61.8 °C (−79.2 °F) and freezes at −71 °C (−96 °F). On further cooling, solid radon glows with a soft yellow light that becomes orange-red at the temperature of liquid air (−195 °C [−319 °F]).
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