Heaviest gas

Radon, with an atomic number of 222, belongs to the group of elements called the noble gases, which means it is chemically inert and unreactive. At room temperature and pressure, 1 m³ (35 ft³) of radon would weigh 9.73 kg (21 lb 7 oz)– more than 100 times what 1 m³ (35 ft³) of hydrogen would weigh. The heaviest non-elemental gas is tungsten hexafluoride, with a density of 13.1 kg/m³ (28 lb 14 oz/35 ft³).