2 ml each of concentrated HCl, HNO₃, and a mixture of concentrated HCl and concentrated HNO₃ in the ratio of 3:1 was taken in test tubes labeled as A, B, and C. A small piece of metal was put in each test tube. No change occurred in test tubes A and B but the metal got dissolved in test tube C respectively. The metal could be

 

Aqua regia is the mixture provided to test the metals in test tubes A, B, and C in accordance with the inquiry. Gold can be dissolved using a solution of three parts concentrated hydrochloric acid and one part concentrated nitric acid (Aqua regia - 3:1 ratio).b

Only aqua regia can dissolve the metal gold; diluted acids cannot dissolve it.