The coordination number is 6. The outer Cl- ion isn't included, so you count 4 x NH3 and 2 x Cl- are within Co's coordination sphere.
Anything that has mass and volume (takes up space) is called matter.
1) it explains about stability of an atom by including stationary state.
2) it explains tge quantization of energy.
3) it gives the concept of angular momentum of a revolving electron.
