OXYGEN (O2) is a gas heavier than air, colorless, odorless and taste free.
ACETYLENE (C2H2) is a slightly lighter than air, flammable, colorless gas, with a distinct garlic–like odor.
ARGON (Ar) is a slightly heavier than air, colorless and odor free gas.
ARGON - CO2 mixtures are very useful in MIG/MAG welding as shielding gases.
NITROGEN (N2) is a colorless, tasteless, and an odorless inert gas, slightly lighter than air; it is used for purging tanks and pipelines and for the removal of moisture from refrigeration systems.