Question

how to find oxidation number?

Answer 1

oxidation number for an atom in its elemental state is zero
oxidation of monovalent atom=charge of the monoatomic ion
1A=+1
2A=+2
3A=+3
4A=+4
5A=-3
6A=-2
7A=-1
8A=0

Answer 2

The sum of the oxidation states of all the atoms in an ion is equal to the charge on the ion.