What is the #"oxidation number"#?
Oxidation number is the charge left on the central atom, when all the bonding pairs of electrons are removed, with the charge assigned to the most electronegative atom.........
And you have forgotten the oxidation state of the oxygen we are breathing in now,
Oxygen is in fact more electronegative than most elements, and thus for many compounds, e.g.
In peroxides, e.g.
So why? Well, remember that our ideas of oxidation numbers are a conceptual label of convenience. They are a useful way of understanding how elements combine, especially in regard to redox reactions, but they do not have fundamental significance.