any of the more than 100 known substances (of which 92 occur naturally) that cannot be separated into simpler substances and that singly or in combination constitute all matter

a fluid in the gaseous state having neither independent shape nor volume and being able to expand indefinitely

a colorless and odorless inert gas; one of the six inert gases; comprises approximately 1% of the earth's atmosphere

a very light colorless element that is one of the six inert gasses; the most difficult gas to liquefy; occurs in economically extractable amounts in certain natural gases (as those found in Texas and Kansas)

a colorless element that is one of the six inert gasses; occurs in trace amounts in air

a colorless odorless gaseous element that give a red glow in a vacuum tube; one of the six inert gasses; occurs in the air in small amounts

a radioactive gaseous element formed by the disintegration of radium; the heaviest of the inert gasses; occurs naturally (especially in areas over granite) and is considered a hazard to health