How do you determine the oxidation state of an element?
Oxidation number is the charge left on the central atom or element, when all the bonding pairs of electrons are removed, with the charge going to the central atom.
Remember that entire exercise is a formalism, that does not have any real existence. Assignment of formal oxidation states can be useful in certain circumstances.
Given this definition the oxidation number of an ELEMENT, which has undergone neither oxidation NOR reduction, is
What has been oxidized, what has been reduced? What about for,
Remember that for element-element bonds, the electrons of the bond are shared between the atoms.