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).

Answer

7

Explanation

`underset((A))(3MnO_2)+6KOH+KCIO_3oversetDeltatounderset((B))(3K_2MnO_4)+KCl+3H_2O`
In presence of `CO_2`, the medium becomes acidic.
`3MnO_4^(2-)+4H^(+)toMnO_2 + 2MnO_4^(-)+2H_2O`
`underset((C ))(MnO_4^-)+5Fe^(2+)+8H^(+)toMn^(2+)+5Fe^(3+)+4H_2O`