How to Find Oxidation Number

An oxidation number is a number assigned to an element that represents the number of electrons lost or gained by an atom of that element in the compound. it is the hypothetical charge.
Oxidation states are represented by integers, that can be positive, negative, or zero. In some cases, the average oxidation state of an element is a fraction number.

There are certain rules to find the oxidation number:
1. Free, uncombined elemental atoms and homoatomic molecules always have an oxidation number of 0. For example, Al, each .
2. Monoatomic ions have an oxidation state equal to the charge on them. For example, the Oxidation number of Al³⁺ is +3 and the oxidation number of Cl⁻ is –1.
3. The hydrogen atom (H) exhibits an oxidation state of +1. It also exhibits an oxidation state of –1 when bonded to active metals such as Li, Na, etc as hydrides.
4. Oxygen has an oxidation of -2 in most of its compounds. However, in the case of peroxides, the oxidation number corresponding to oxygen is –1. It also exhibits oxidation states +1 and +2 in O₂F₂and OF₂.
5. The oxidation number of a Group 1 element in a compound is +1.
6. The oxidation number of a Group 2 element in a compound is +2.
7. Halogens have a -1 oxidation number when combined with one other element (binary compounds), except for inter-halogen compounds.
8. The algebraic sum of oxidation states for all atoms in a neutral molecule must be zero.
9. The sum of the oxidation numbers in a polyatomic ion is equal to the charge of the ion.
For example, in a sulfite ion (SO₃^2-), the total charge of the ion is 2, and each oxygen is assumed to be in its usual oxidation state of -2. Because there are three oxygen atoms in sulfite, oxygen contributes 2