Argon is an element in the periodic table with the symbol Ar and atomic number 18. It is the third most abundant element in the atmosphere of Earth, at a concentration of about 0.934%. Argon is a colorless, odorless, and tasteless gas that is chemically inert. It is used in a variety of applications, including as a shielding gas in welding, as an inert gas in light bulbs, and as a refrigerant.