Aqua regia is a latin word for royal water. It is a special liquid which can dissolve noble metals like gold, platinum, palladium. Gold usually does not react with other chemicals. Aqua regia is a mixture of two acids and it does not have a chemical formula. However it can be represented by HNO3 + HCL which indicates hydrochloric acid and nitric acid. Aqua regia is used for purification purpose of gold and platinum.