Radon

Radon (IPA: /ˈreɪdɒn/) is a chemical element in the periodic table that has the symbol Rn and atomic number 86. A radioactive noble gas that is formed by the decay of radium, radon is one of the heaviest gases and is considered to be a health hazard. The most stable isotope is 222Rn which has a half-life of 3.8 days and is used in radiotherapy. Radon is a significant contaminant that affects indoor air quality worldwide. Radon gas from natural sources can accumulate in buildings and reportedly causes 21,000 lung cancer deaths per year in the United States alone.