Radon is colourless and odourless formed by the radioactive decay of the small amounts of uranium that occur naturally in all rocks and soils.
Nid oes gan radon liw nac arogl ac mae’n cael ei ffurfio wrth i symiau bach o wraniwm sydd i’w gael yn naturiol mewn creigiau a phridd ddadfeilio’n ymbelydrol.