_______ + heat ⟶K2MnO4+MnO2+O2
On the product side, we have
2 K atoms, 2 Mn atoms and 8 O atoms
We know that the atoms on the reactant side should be the same as on the product side.
So, on balancing we get:
KMnO4 is potassium permanganate.
This is the laboratory method to prepare O2.