| Answer | Crossword Clue |
|---|---|
| radon | a heavy radioactive gaseous element formed by the decay of radium see element table |
| radons | inert radioactive gaseous element produced by the decay of radium |
| radon | inert radioactive gaseous element produced by the decay of radium |
| xenon | a heavy colorless and relatively inert gaseous element that occurs in air as about one part in 20 million and is used especially in specialized electric lamps (as flashtubes) and in scientific research see element table |
