hydrogen

A colorless, highly flammable gaseous element, the lightest of all gases and the most abundant element in the universe, used in the production of synthetic ammonia and methanol, in petroleum refining, in the hydrogenation of organic materials, as a reducing atmosphere, in oxyhydrogen torches, and in rocket fuels. Atomic number 1; atomic weight 1.00794; melting point -259.14°C; boiling point -252.8°C; density at 0°C 0.08987 gram per liter; valence 1. See Table at element.