Hydrogen, or H2, is the lightest of all gases. Commonly found in nature in compounds with other elements, it is the most abundant element in the universe.

Hydrogen is a component of water, minerals and acids, as well as an essential part of all hydrocarbons and essentially all other organic substances. In fact, 98 percent of the known universe - most notably the sun and stars - consists of hydrogen.

Colorless, odorless, tasteless and nontoxic, hydrogen exists as a gas at atmospheric temperatures and pressures. A stable molecule because of its high bond strength, hydrogen becomes reactive at elevated temperatures or with the aid of catalysts. When cooled to its boiling point of -423°F (-253°C), hydrogen becomes a liquid that is approximately 93 percent lighter than water. All other gases - except helium - become solids at this temperature.

Hydrogen is flammable and burns in air with a pale blue, almost invisible flame. In its gaseous form, hydrogen dissipates quickly. These unique properties call for strict safety measures in hydrogen use and storage.