A black compound (A) is solid state is fused with KOH with `KClO_3`.The aqueous extract of fused mass is green colour solution (B).On passing `CO_2` gas through it pink colour of ( C) is noticed along with some black insoluble mass of (A).The pink coloured solution is decolourised by `Fe^(2+)` in acidic medium.What is oxidation state of central metal in ( C).