Helium
Helium is less dense than any other known gas except hydrogen and is about one seventh as dense as air. Extremely unreactive, it is an inert gas in group 0 of the periodic table . Natural helium is a mixture of two stable isotopes, helium-3 and helium-4. Helium is colorless, odorless, tasteless and non-toxic. It heads the noble gas series in the periodic table. Helium has the lowest boiling and melting points among the elements. For commercial purposes, helium is used in cryogenics, deep-sea breathing systems, to cool superconducting magnets, in helium dating, for inflating balloons and as a protective gas for many industrial uses, such as arc welding.