Radon is a chemical element (symbol Rn and atomic number 86). It is a radioactive, colorless, odorless, tasteless gas, occurring naturally as the decay product of radium. It is one of the heaviest substances that remains a gas under normal conditions and is considered to be a health hazard due to its radioactivity. Its most stable isotope 222Rn , has a half life of 3.8 days. Due to its high radioactivity, it has been less well-studied by chemists, but a few compounds are known.