For balancing a redox reaction by oxidation number method, follow the order of steps as lisled below (of course, all steps may not be required for balancing some reactions).

(i) For each redox reaction, deduce the oxidation state of the elements that are undergoing oxidation and reduction.

(ii) Separate the reactants and products into two half reactions involving the elements that change their oxidation state. Write the skeletal equations for each half- reaction.

(iii) For each half- reaction, first balance the number of atoms of the element undergoing change in oxidation state.

(iv) Now find the total change in oxidation number by determining the change per atom and multiplying it by the total number of atoms that undergoes change. Also, decide whether electrons are lost or gained. An increase in oxidation state is loss of electrons and a decrease in oxidation state is gain of electrons.

(v) Add the electrons lost or gained to the half equation. Lost electrons are placed on the product side and gained electrons are kept on the reactant side.

(vi) Now add both the half reactions after multiplying by suitable integers to make the number of electrons lost and gained same.

(vii) Transfer the coefficients of each reactant and product to the main skeleton equation.

(viii) If the coefficients developed are not correct, then change them by inspection. Such coefficient changes are required when an
element from a compound goes in `2` different compounds. one with the same oxidation state & the other with different oxidation state.

(ix) Count the charges on both sides of the equation and balance the charges in the equation by adding requisite `H^+` or `OH^-` to the required side. If the reaction occurs in acidic solution, use `H^+` and if it occurs in basic solution. use `OH^-`. If the reaction occurs in neutral solution, use `H^+` or `OH^-` on any of the side as needed i.e. in a neutral solution, if negative charges are needed for balancing, use `OH^-` and if positive charges are needed, use `H^+`.

(x) Balance the hydrogens and oxygens by adding the appropriate number of `H_2O` molecules on the required side.

This method of balancing redox reaction involves following steps:

(i) For each redox reaction. deduce the oxidation state of the elements that are undergoing oxidation and reduction.

(ii) Separate the reactants and products into two half-reactions involving the elements that changes its oxidation state. Write the skeleton equations for each half- reaction.

(iii) Balance each half-reaction separately involving given steps.

a) First balance the atoms of the element undergoing oxidation or reduction.
b) Then balance atoms of the elements other than hydrogen and oxygen.
c) For balancing oxygen atoms in acidic or neutral medium, add suitable number of `H_2O` molecules to the side deficient in `O` while in alkaline medium, add equal number of `H_2O` molecules as the excess of `O` on the side having excess of `O` atoms and add double the number of `OH^-` ions on the opposite side of the equation.

d) In order to balance the hydrogen atoms in acidic or neutral medium, add required number of `W` to the side deficient in `H` while in alkaline medium, add equal number of `OH^-` ions as the excess number of `H` atoms on the side having excess `H` and add equal number of `H_2O` molecules on the opposite side of the equation.

e) Multiply each half-reaction by suitable integer to make the number of electrons lost and gained same and add both the half-equations to get a completely balanced reaction.