Xenon

Xenon originates from the Greek word for 'strange'- and strange it is. Discovered by Sir William Ramsay and M. W. Travers of England in 1898, xenon is a noble or inert gas. The thing that makes it strange is that it is in fact the heaviest gas currently known- a liter of it weighs 5.842 grams. Even though it is a gas, it still forms compounds. While xenon itself isn't toxic, it's compounds ARE.

That is only one of the differences between the compound and gas. Compounds can be colored, while most gas stays colorless. However, excited xenon in a vacuum tube glows blue. Xenon is often used in electron tubes, bactericidal lamps, strobe lamps, and lamps used to excite ruby lasers. It is often obtained by extraction from liquid air. However, other "xenons" are produced by neutron irradiation in air cooled nuclear reactors.