5 mL each of concentrated HCl, HNO3 and a mixture of concentrated HCl (15 mL) and concentrated HNO3 (5 mL) were taken in test tubes labelled 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. The
metal could be
(b). Gold (Au) dissolves in aqua regia.