Possible Clues:

• Helium or neon
• Such as neon or xenon
• One's stable, though angriest when unstable
• Angriest outpouring from one at the edge of a table
• He is the lightest one
• Neon sign at heart of eery flickering
• Xenon or neon
• ANAGRAM #2 (with 47-across)
• It's argon? Neon? Neither taking on being reactive
• Krypton, e.g.