Rules of oxidation number??? ???

Rules:

• Oxidation number of free element is always ZERO
• Example: The oxidation number of atoms in O₂, H₂ and N₂ = 0
• The oxidation number of Hydrogen is +1
• Exception: In Metal hydrides the oxidation state of hydrogen is -1
• The Oxidation state of IA group elements = +1
• The oxidation state of IIA group elements = +2
• The oxidation number of IIIA group elements = +3
• The oxidation state of Oxygen = -2
• Exception: The Peroxides and super oxides the oxidation state is -1, -1/2 respectively
• The oxidation state of VIIA group elements = -1
• Exception: In inter halides the oxidation state will differs
• In neutral compound the sum of oxidation numbers of all the atoms = 0
• In polyatomic ions the sum of the oxidation number is equal to charge on the ion
• Example: Hydroxide ion (OH-) the oxidation number = -1