Related Clues:

• Oxygen and helium, for instance
• Substances that are not solidor liquid
• Hydrogen and carbon monoxide, say
• Symbolically N and H, for instance
• H, O and N, in short
• Symbolically N and O, for instance?
• Gee! That's how 35 across without any tea is the death of you
• Eleven of the elements, under normal conditions
• Argon and xenon, for two
• Causes of laughter or tears, for example
• Neon and xenon, for two
• Argon and neon, for two
• Unseen elements
• Krypton and methane
• Fills (up), as a car