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hydrogen(hi'dro-jen) [ hydro- + -gen] H
Hydrogen is present in the sun and stars. Even though it is the most abundant element in the known universe, its concentration in the earth's atmosphere is only 0.00005%. Hydrogen occurs in its free state (in natural gases and volcanic eruptions) only in minute quantities. It occurs principally on the earth as water (hydrogen oxide, H2O) and is a constituent of all hydrocarbons. Hydrogen is present in all acids and in ionic form is responsible for the properties characteristic of acids. Hydrogen is present in nearly all organic compounds and is a component of all carbohydrates, proteins, and fats.
It is highly flammable and used in the oxyhydrogen flame in welding, in hydrogenation of oils for solidifying purposes, as a reducing agent, and in many syntheses.
hydrogen cyanideHydrocyanic acid.
hydrogen dioxideHydrogen peroxide.
hydrogen iodideHydriodic acid.
It is used as a commercial bleaching agent; as an oxidizing and reducing agent; and, in a 3% aqueous solution, as a mild antiseptic, germicide, and cleansing agent.