An inert gas is any gas that, in a given circumstance, is not reactive. For instance molecular nitrogen is often used as an inert gas in food packaging to ensure that food does not spoil in transit.

Helium, neon and argon are the only true elemental inert gases as they do not form any true compounds with other elements like the heavier noble gases.

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An inert gas was also the former term for the elements of Group 8A (IUPAC notation: 18) of the periodic table, now referred to as noble gases.

See also: inerting system