Argon
Liquid argon is used in neutrino experiments and looking for dark matter. Argon is used to preserve food. Argon is sometimes used as the propellant in aerosol cans. Argon is also used as a preservative for such products as varnish, polyurethane, and paint. Argon has been used by athletes as a doping agent and has been banned as use. It is used to know how old rocks are.