Densest element to remain a gas in free air

Radon (given the symbol Rn and atomic number 86) is the heaviest of the naturally occuring noble gases on the Period Table. Its density is around 9.73 kg/m3, about eight times the density of Earth's atmosphere at sea level (1.217 kg/m3). Radon was discovered in 1900 by German physicist Friedrich Ernst Dorn (27 July 1848–16 December 1916) and is a colourless, odorless, tasteless gas that also has the distinction of being the only radioactive gas under normal atmospheric temperatures and pressures. Radon's most stable isotope possesses a half-life of only 3.8 days and the products of its decay are solids that stick to the surfaces of airborn dust particles. If inhaled by humans, these contaminated dust particles increase the risk of lung cancer.