Related Clues:

• The first two periodic table entries
• Neon and argon
• Krypton and others
• Rightmost column in the periodic table
• Hydrogen and oxygen, e.g.
• Fills (up)
• Neon and others
• Oxygen and helium, for instance
• Hydrogen and carbon monoxide, say
• Symbolically N and H, for instance
• H, O and N, in short
• Symbolically N and O, for instance?
• Eleven of the elements, under normal conditions
• Argon and xenon, for two
• Causes of laughter or tears, for example