Question
Balance the following redox reaction by oxidation number method:
Solution
(i) The skeleton equation along with oxidation number of each atom is
(ii) Noting the change in O.N. of above atoms,
Increase in Cr = + 3 to +6 i.e.
Decrease per atom of O = 1 (from O in H2O2 to O in H2O)
Total number of O atom involved = 2
Total decrease for 2 atoms of O = 2 x 1 = 2
(iii) Equalise the increase/decrease in O.N. by multiplying H2O2 by 3 and 
(iv) 
