The chemical formula of argon is Ar, CAS number 7440-37-1. It is a colorless, odorless and tasteless inert gas under normal temperature and pressure. Its liquid form is a colorless and transparent liquid. The boiling point under standard atmospheric pressure is -185.9°C, the critical temperature is 150.8K, and the density is about 1.40g/cm3 (at -185.9°C). It is extremely difficult to dissolve in water and is much denser than air. It is the most abundant rare gas in the air. It is extremely inactive in chemical properties and generally does not react chemically with other substances. It can only form a few compounds under special conditions. It is mainly used as protective gas in industry, such as metal welding, semiconductor manufacturing, and light bulb filling; it is also used in low-temperature refrigeration, gas chromatography analysis, and can be used as an inert environmental carrier in scientific research fields.