xenon

Colourless, odourless, gaseous, non-metallic element, atomic number 54, relative atomic mass 131.30. It is grouped with the noble gases (rare gases) and was long believed not to enter into reactions, but is now known to form some compounds, mostly with fluorine. It is a heavy gas present in very small quantities in the air (about one part in 20 million).

Xenon is used in bubble chambers, light bulbs, vacuum tubes, and lasers. It was discovered in 1898 in a residue from liquid air by Scottish chemists William Ramsay and Morris Travers.