Argon

An chemical element, in the periodic table Argon has the symbol Ar and atom number 18.

One of the [noble gases]? in period 8, diatomic Argon makes up about 1% of the Earth's atmosphere. It is used in lighting as it will not react with the filament in a lightbulb? even under high temperatures, and other cases where Nitrogen is an unsuitable (semi-)inert gas.