Hydrogen is the most abundant element in the universe. It is the main component of stars and gaseous planets.
In general, hydrogen is rarely found in its pure state, especially on Earth. It is generally combined with other atoms such as oxygen in water (H2O) or carbon in hydrocarbons (CH4, C2H6, …).

It can be found in gaseous form when two hydrogen atoms are combined – we speak then of “dihydrogen” – and in liquid form when the gas has been cooled to -252.87°C.