Classification of Matter

In the shells of atom, there are an (a)  

In the (a)   of atom, there are protons and neutrons.

This picture is the example of (a)  

This picture is the example of (a)  

The atomic number of Ge (a)  

The mass number of Ge ...

(a)  

The number of electron of atom Ge (a)  

The number of neutron of atom Ge (a)  

The number of proton of atom Ge (a)  

The maximal number of electron in the first shells (K shells) (a)