<p><strong>Noun</strong></p><ul><li>a colorless, odorless, gaseous element constituting about one-fifth of the volume of the atmosphere and present in a combined state in nature.</li><li>it is the supporter of combustion in air and was the standard of atomic, combining, and molecular weights until 1961, when carbon 12 became the new standard.</li><li>Symbol: O</li><li>Atomic weight: 15.9994</li><li>Atomic number: 8</li><li>Density: 1.4290 grams/liter at 0°C and 760 millimeter pressure.</li></ul>