What name is given to those metal oxides which show basis as well as acidics behavior ?

9 What is aqua-regia ? Name two special metals which are insoluble in comman reagents but dissolve in aqua-regia. 10 Give the names and formulae of (a) two acidic oxides, and (b) two basis oxidics. 12 Name two metals which form amphoteric oxides. 13 A copper coin is kept immersed in a solution of silver nitrate for some time. What will happen to the coin and colour of the solution ?