atomic number 5
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|Noun||1.||atomic number 5 - a trivalent metalloid element; occurs both in a hard black crystal and in the form of a yellow or brown powder|
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
borax - an ore of boron consisting of hydrated sodium borate; used as a flux or cleansing agent
kernite - a light soft mineral consisting of hydrated sodium borate in crystalline form; an important source of boron