Oxidation number is not equal to number of electrons accepted or donated by an atom.
Valency is the number of protons an atom can donate or accept to form a chemical bond with another atom.
Reduction is the process in which an atom (or ion) donates an electron or hydrogen ion reducing its oxidation number.
‘Valency is also the number of electrons -donated or accepted by an atom so as to achieve the stable electronic configuration of the nearest noble gas’.With reference to this definition.
b) State why the valency of-
(ii) Chlorine,oxygen,and nitrogen is : -1,-2, &-3 respectively.