Rusting is where oxygen binds to iron and forms iron oxide.
So once iron rusts, there is oxygen, just not in air; it's in the iron oxide.
All reactions are reversible, albeit at different rates (the "irreversible" ones are still reversible, but much slower given that they take so much collision luck and energy.
The number of protons also determines the identity of the element. ... Since the atom is electrically neutral, the number of electrons must equal the number of protons.
