Oxidation state does not necessarily have a physical basis.
Following a set of rules, oxidation state for any atom in a
substance can be determined.
Oxidation is increase in oxidation state while reduction is
decrease (reduction) in oxidation state.
That which undergoes oxidation is the reducing agent while that
which undergoes reduction is the oxidizing agent.
Or
that which oxidizes another substance is the oxidizing agent, that which reduces
another substance, the reducing agent.
Redox reactions can be represented using half-equations.
Oxidation number allows us to balance redox reactions.
Notice that some reaction that we considered before (such as
metal-acid reaction) can also be classified as a redox
reaction; in other words, these classifications arenīt hard a
fast.