Hydrogen (H2) makes up 98% of the known universe, and it is the third most abundant
element on the earth's surface.
It is the lightest of all the gases, with a gaseous specific gravity of 0.0695. It is a component of water, minerals and acids, and it makes up a fundamental part of all hydrocarbons and organic substances.
At atmospheric temperatures and pressures, hydrogen exists as a gas; however, it liquefies at -252.9°C (-423°F). Next to helium, it is the coldest known fluid.
Hydrogen is one of the materials now being considered as an alternative fuel because it is renewable, abundant, efficient, and unlike other alternatives, produces zero emissions. Many believe that this versatile material will become a primary fuel and energy carrier of the future.