(a) Oxidation number refers to the number of charges an atom would have in a molecule or an ionic compound, if electrons were transferred completely.
(b) Rules to assign oxidation number:
\(\bullet\) Oxidation number of a substance in its elementary state is equal to zero (H2, Br2 , Na)
\(\bullet\) Oxidation number of a mono-atomtic ion is equal to the charge on the Ton (Na4 =+ 1,
\(\bullet\) Oxidation number of hydrogen in a compound is +1 (except hydrides).
\(\bullet\) Oxidation number of hydrogen in metal hydrides is -1 (NaH, CaH2).
\(\bullet\) Oxidation number of oxygen in a compound is -2 (except OF2 and peroxides).
\(\bullet\) Oxidation number of oxygen in peroxides is -1 (He,, Na»,) = I.
\(\bullet\) Oxidation number of oxygen in fluorinated compounds is either +1 or +2.(OF2 = +2, O,F2 + 1).
\(\bullet\) Fluorine has an oxidation number -1 in all ìts compounds.
\(\bullet\) The sum of the oxidation number of all the atoms in neutral molecules is equal to Zero.
\(\bullet\) For all ions, the sum of the oxidation number of all atoms is equal to the charge of the ion.
