nary, stable form of the element. There are two other allotropes (solid forms)--yellow arsenic and black arsenic, whose modifications have no metallic properties. Occasionally found free in nature, arsenic usually occurs in combination with sulfur, oxygen or certain metals like cobalt, copper, nickel, iron, silver, and tin. In combination, such arsenic is referred to as inorganic arsenic. Arsenic combined with carbon and hydrogen is referred to as organic arsenic. The organic forms are u
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