Dear Fajrul,

There are at least three points you have to embrace in order to make quick progress in sciences. It would be good that you talk to your teachers to discuss them to understand how they personally and in public life deal with them. What is important that they spent some time in the classroom to teach them too.

1) What we learn and are thought are only the digests of concepts. This is equivalent with what we in physics call a model. The role of model (which is sometimes a higher level of abstraction or sometimes idealization, or sometimes omission) makes the learning possible. So both MnO2 nad MnO6 are only models and you need to know the extend of applicability of both.

2) Sometimes a model situation leads to difference in interpretation depending on the context. MnO2 belongs to the well balanced chemical, quantum, electrostatic, model of an ion Mn2+ in solution (which on its own is also a model), versus another model of oxygen bound to this ion. MnO6 is an idealized unit of unbalanced coordination where you pack small balls of different radius to form an octahedral complex . All of these descriptions are all a variable level of a model. Balls are not balls in QM atomic interpretations. Charge is not charge but probability distribution. Electron is not a particle but also a wave, etc. etc. etc.

3) If you look close r at your beautiful pictures you suddenly discover that the reality always lurks behind them. Many position of oxygens are interacting with other ions (are shared) therefore you suddenly realize that both MnO2 and MnO6 are only artifacts of the language of description. The rules of science (physics) requires as much charge and mass averaging as possible and therefore all of them are smeared out over the entire structure. I also suspect that your beautiful pictures omit some ordered and disordered other types of atoms.

Please study a bit crystallography that is behind these beautiful pictures and understand the role of occupancy, and notion of a unit cell, and special positions.

Good Luck in your studies.

Bog