A gaseous element, colorless, tasteless, and odorless, the lightest known substance, being fourteen and a half times lighter than air (hence its use in filling balloons), and over eleven thousand times lighter than water. It is very abundant, being an ingredient of water and of many other substances, especially those of animal or vegetable origin. It may by produced in many ways, but is chiefly obtained by the action of acids (as sulphuric) on metals, as zinc, iron, etc. It is very inflammable, and is an ingredient of coal gas and water gas. It is standard of chemical equivalents or combining weights, and also of valence, being the typical monad. Symbol H. Atomic weight 1.

simplest atom, consisting only of one proton and one electron; the most abundant element in the Universe.

the lightest known gas; hydrogen vapors are highly flammable, colorless, odorless, tasteless, and nontoxic. Hydrogen is used as a means of providing a reducing atmosphere, as a carrier gas for epitaxial processes, and as a reagent to produce high-purity water. It sometimes is used in gas mixtures of fluorine-based plasma etchant for the processing of silicon dioxide film. Also see dry plasma etch.

An in flammable, colorless, odorless, gaseous chemical element the lightest of all known substances.