1.oxidaton number for an elemnt or compound in its free state is zero
2.elemnt or compound with ion whether monoatomic or diatomic has same oxidation number as the ion.
3.the sum of all oxidation numbers in a neutral compound is zero.4.for alkali metal O.N is +1 nd for alkali earth metal it is +2.5.usually oxygen O.N of -2 but for peroxides it is -1 nd for superperoxides it is +1.6.for halogens O.N is always -1.