Question

How are oxidation numbers assigned?

Answer 1

See here and enclosed links.

Explanation:

`"Oxidation number"` is the charge left on the central atom, when all the bonding pairs of electrons are removed sequentially with the charge, the electron, assigned to the most electronegative atom. The idea of electron transfer in oxidation reactions is a bit abstract in that we invoke `"electrons"` as virtual particles. The approach does work.