When an oxide of manganese (A) is fused with KOH in the presence of an oxidising agent and dissolved in water, it gives a dark green solution of compound (8). Compound (8) disproportionates in neutral or acidic solution to give purple compound (C). An alkaline solirtion of compound (C) oxidises potassium iodide solution to a compound (D) and compound (A) is also formed. Identify compounds A to D and also explain the reactions involved.
Thinking Process

This problem based on the concept of preparation and properties of potassium permanganate.

NEETprep Answer: |tis the method of preparation of potassium permanganate (purple).
Thus, (A) = MnO2                 (B) = K2MnO4
           (C) = KMNO4              (D) = KIO3

   2MnO2 + 4KOH + O2  2K2MnO4 + 2H2O
     A                                             B    
       3MnO42- + 4H+  2MnO4- + MnO2 + 2H2O
2MnO4- + H2O + KI  2MnO2 + 2OH- + KIO3
                                               A                             D