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Gold doesn't react with acid, with the exception of aqua regia which is concentrated nitric and hydrochloric acids combined. It's one of the "noble metals" and the least reactive of the metals. It has a standard reduction potential of +1.56V, compared to the hydrogen reference cell which is 0. Since gold has a higher potential to be reduced than hydrogen, H+ isn't likely to oxidize it.
Oxidation and reduction refer to transfer of electrons. For gold to be oxidized and H+ (acid) to be reduced electrons would have to be transerred from gold to hydrogren. This wouldn't be energetically favorable based on their reduction potentials. The reason gold dissolves in aqua regia is because it forms AgCl3 with the Cl that's liberated by the reaction between HCl and HNO3.
Gold's property of resisting corrosion makes it useful for coins and jewelry.
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