Explain the preparation of Potassium pemanganate ?

When manganese dioxide is fused with potassium hydroxide in the presence of air or an oxidising agent such as potassium nitrate or chlorate, potassium manganate is formed, possibly via potassium manganite.

 

                                                  _fused

            MnO₂ + 2KOH ––––––?    K₂MnO₃          +    4H₂O] × 2

                                                              ^{potassium manganite}

            2K₂MnO₃ + O₂ ––––––? 2K₂MnO₄ + 2H₂O

                                                             _fused

            2MnO₂ + 4KOH + O₂ ––––––? 2K₂MnO₄ + 2H₂O

            ^{pyrolusite                                     potassium manganate}