atomic number 85
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|Noun||1.||atomic number 85 - a highly unstable radioactive element (the heaviest of the halogen series); a decay product of uranium and thorium|
chemical element, element - any of the more than 100 known substances (of which 92 occur naturally) that cannot be separated into simpler substances and that singly or in combination constitute all matter
halogen - any of five related nonmetallic elements (fluorine or chlorine or bromine or iodine or astatine) that are all monovalent and readily form negative ions