The _ _ states that electrons fill orbitals starting at the _ energy level and building themselves _ to higher energy levels.

It is a mixture. simply put, a compound must be pure, that is, of only one chemical structure and composition. a mixture is made of different chemical substances (i.e. elements, molecules, compounds) that are not chemically bonded to each other, but instead physically grouped together, as in the case of gasoline (a homogeneous solution).

It will appear as o2(g) as a reactant 

The answer is conduction

It starts to rust i think