Hydrogen 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.

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