raregas Neon, e.g Krypton, e.g Xenon, for one Xenon, e.g Helium, for one Neon or argon Xenon or krypton Noble element Krypton or xenon Erstwhile name for a "noble" element Element such as helium, neon etc Element on the far-right side of the periodic table Krypton, e.g. Krypton, for one 37-Across, e.g. Neon, for one Relatively piquant One highly unlikely to react 21-Across, e.g. Noble one Noble at the end of a table? "Noble" thing Last-column element on the periodic table