Taking the example of methanol show that the oxidation number of carbon is not the same as its valency.Chemistry
Let's define the two different terms talked about here. The valency of an atom is the maximum number of covalent bonds that it can form with other atoms. The oxidation number of an atom is the number of bonds it has with more electronegative atoms, usually oxygen. For the example of methanol, the chemical formula for methanol is CH3OH. There is a central carbon atom that has four single bonds attached to it; three to hydrogens and one to a hydroxyl group (OH) oxygen. The valency of carbon is four. It can form four covalent bonds to other atoms via its sp3 hydridized orbitals. The oxidation number of the carbon in this case is one. The three hydrogen atoms are not electronegative and the one oxygen atom is electronegative. So to summarize, for the carbon in methanol the valency number is 4 and the oxidation number is 1.