Hydrogen is the most abundant element in the universe but on Earth it is generally found in compounds. It has three isotopes - protium, deuterium, and tritium which is radioactive. Hydrogen is produced industrially mainly through steam reforming of hydrocarbons. It is used to make ammonia via the Haber process and for hydrogenation of oils. Noble gases are very unreactive and occur rarely in the atmosphere, though some like helium are used for balloons and breathing mixtures for divers.