| Answer | Crossword Clue |
|---|---|
| GAS | Hydrogen or neon |
| GASES | Neon and hydrogen |
| GAS | Oxygen or hydrogen |
| GAS | Hydrogen or helium |
| GAS | Hydrogen or nitrogen. |
| ELEMENT | Hydrogen or oxygen. |
| ELEMENT | Hydrogen or helium |
| ELEMENT | Helium or hydrogen |
| GAS | Helium or hydrogen |
| ATNO | 1 for hydrogen or 2 for helium: Abbr. |
