A coloured solution known to contain two metal ions of different groups, was treated with excess cold sodium hydroxide solution. When filtered a whitish solid, slowly changing to brown, was retained on the filter paper and a colourless solution collected as the filtrate. Drop wise adition of hydrochloric acid to the filtrate produced a white precipitate which dissolved in excess acid. Treatment of the residue from the filter paper with a strong oxidiser, `PbO_(2)` and concentrated `HNO_(3)` on boiling produced a reddish-violet (purple) solution.
Reddish-violet solution obtained by oxidation is of:
A. `ZnO_(2)^(2-)`
B. `MnO_(4)^(2-)`
C. `MnO_(4)^(-)`
D. `MnO_(2)`
