Balance the following redox reaction by ion-electron method:

The skeleton equation is:

Separation of the equation in two half reactions
(i) Write the O.N. of the atoms involved in the equation
   -7 -2           -1                 +4 -2    0
    
(ii) Identify the atoms which undergo a change in O.N.
    +7        -1                    +4         0

(iii) Find out the species involved in the oxidation and reduction half-reactions:

Oxidation half-reaction:
                   
Reduction half-reaction:
               
Balancing the oxidation half reaction
                    
Balancing the reduction half reaction
 The reduction half-reaction is:
                       
(i) As the decrease in O.N. is 3, therefore add 3e^- on the reactant side
                             
(ii) Balance O atoms by adding two H₂O molecules on the product side 
               
(iii) Balance the charges, by adding four OH- on the product side and balance H atoms by adding four H2O molecules on the reactant side. 
      Thus, the reduction half-reaction is balanced. Adding the two half reactions. In order to equate the electrons, multiply equation. (i) by 3 and equation, (ii) by 2 and add the two equations.