Hydrogen (H):
A colorless and odorless gaseous element. The lightest and apparently the most abundant chemical element in the universe. However, it is found only in trace quantities in the observable portion of our atmosphere, only about 0.00005 percent by volume of dry air. Hydrogen has a molecular weight of 2.0160 and specific gravity referred to air of 0.0695. At one time hydrogen was the commonly used inflation gas for meteorological balloons, but because of its dangerous combustibility, it has been largely replaced by helium.
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