Related Clues:

• Krypton, e.g.
• Noble one
• Xenon, for one
• Neon, for one
• Krypton, for one
• Helium, for one
• Xenon or krypton
• Last-column element on the periodic table
• 49-Down, for example
• Start to rouse a man when one hardly ever reacts
• Element such as helium, neon etc
• 21-Across, e.g
• Krypton, e.g
• One highly unlikely to react
• Xenon, e.g