Radon is a
chemical element with symbol
Rn and
atomic number 86. It is a
radioactive, colorless, odorless, tasteless
noble gas, occurring naturally as a
decay product of
radium. Its most stable
isotope,
222Rn, has a
half-life of 3.8 days. Radon is one of the densest substances that remains a
gas under normal conditions. It is also the only gas under normal conditions that only has radioactive isotopes, and is considered a health hazard due to its radioactivity. Intense radioactivity has also hindered chemical studies of radon and only a few compounds are known.