Subtitle: Argon
Argon is a chemical element with the symbol Ar and atomic number 18. It is in group 18 of the periodic table and is a noble gas. Argon is the third most common gas in the Earth's atmosphere, at 0.934% (9340 ppmv). It is more than twice as abundant as the next most common atmospheric gas, water vapor (which averages about 4000 ppmv, but varies greatly), and 23 times as abundant as the next most common non-condensing atmospheric gas, carbon dioxide (400 ppmv). Argon is the most abundant noble gas in Earth's crust, comprising 0.00015% of the crust.
Argon is a colorless, odorless, non-toxic, non-flammable and inert gas. It is mostly used for its inert properties in industrial and laboratory applications. Argon is also used in lighting, and welding. Pure argon gas is a single gas (monatomic), consisting of only one type of atom; therefore, it is a pure gas.
