A metal 'X' normally used for making calorimeters is heated in abundant supply of air until a black coloured residue ' Y' is obtained. This Y reacts with sulphuric acid to form blue coloured salt 'Z'. When to this solution little of ammonium hydroxide was added, pale blue precipitates of 'A' are obtained. This 'A' dissolves in excess of ammonium hydroxide to form a deep blue solution B. Identify the metal X and write the equations for the formation of various compounds i.e., Y, Z, A and B.