A certain inorganic compound (X) shows the following reactions:
(i) On passing H2 S through an acidified solution of (X) a brown ppt. is obtained.
(ii) The ppt. obtained at step (i) dissolve in excess of yellow ammonium sulphide.
(iii) On adding an aqueous solution of NaOH to a solution of (X), first a white ppt. is obtained which dissolves in excess of NaOH.
(iv) The aqueous solution of (X) reduce ferric chloride. Identify the cation of (X) and give chemical equations for reactions at steps (i), (iii) and (iv)