inert gas

noble gas   n.  Any of the elements in Group O of the periodic table, including helium, neon, argon, krypton, xenon, and radon, which are monatomic and with limited exceptions chemically inert. Also called inert gas.

Main Entry: no·ble gas
Pronunciation: 'nO-b&l-
Function: noun
: any of a group of rare gases that include helium, neon, argon, krypton, xenon, andsometimes radon and that exhibit great stability and extremely low reaction rates called also inert gas

noble gas no·ble gas (nō'bəl)
n.
Any of the elements in Group O of the periodic table, including helium, neon, argon, krypton, xenon, and radon, which are monatomic and with limited exceptions chemically inert. Also called inert gas.

noble gas   (nō'bəl)  Pronunciation Key  Any of the six gases helium, neon, argon, krypton, xenon, and radon. Because the outermost electron shell of atoms of these gases is full, they do not react chemically with other substances except under certain special conditions. Also called inert gas. See Periodic Table.