noble gas no·ble gas (nō'bəl)
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.
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.