The noble gases are the six elements in Group 18 (VIIIA) of the periodic table.
The symbol A was used for argon until the 1950s when chemists agreed to use the two letter symbol Ar for the element. Argon changes from a gas to a liquid at -185.86°C (-302.55°F).
One non-radioactive isotope is used, however, to find the age of very old rocks.
This method of dating rocks is described in the potassium entry.
Argon is also used in making "neon" lamps and in lasers. However, English scientist Henry Cavendish (1731-1810) had predicted the existence of argon 200 years earlier.
When Cavendish removed oxygen and nitrogen from air, he found that a very small amount of gas remained.