Gold (pronounced /ɡold) is a chemical element with the symbol Au (Latin: aurum, "shining dawn") and an atomic number of 79. Gold is dense, soft, shiny and the most malleable and ductile pure metal known. Gold is one of the coinage metals and has served as a symbol of wealth and store of value throughout history. Gold standards have provided a basis for monetary policies. Chemically, gold is a transition metal and can form trivalent and univalent captions in solutions. Compared with other metals, pure gold is chemically least reactive, but it is attacked by aqua Regina (a mixture of acids), forming chloral acid, but not by the individual acids, and by alkaline solutions of cyanide. Gold dissolves in mercury, forming alloys, but does not react with it. Gold is insoluble in nitric acid, which dissolves and base metals. Nitric acid has long been used to confirm the presence of gold in items, and this is the origin of the colloquial term "acid test", referring to a gold standardizes for genuine value.
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