Radon comes from under the Earth, and is the sixth and heaviest of the Noble Gases. Also the only one that is unstable – breaking down radioactively into Lead, Bismuth and Polonium, known to chemists as her "decay daughters." Her color is that of phosphorescence, the way her radioactive decay is made visible to the eye. She is accordingly poisonous, though useful if precautions are taken. Her daughters are of mixed virtue: Lead is useful and hard-working, though a moderately toxic heavy metal. Bismuth is entirely salutary and may be ingested without fear. Polonium is deadly and has no redeeming qualities. In every way, Radon is the opposite of Helium.