The oxidation number of chlorine decreases from +7 to +3 and the oxidation number of O  increases from -1 to 0.SO  CI2O7 is oxidizing agent and H2O2 is reducing agent .

ion electron method

the oxidation half reaction is H2O2--->O2

To balance oxidation number 2 electrons are added

H2O2--->O2+2e-

2 hydroxide ions are added to balance the charge

H2O2+2OH---->O2+2e-

2 water molecules are added to balance the O atoms

H2O2+2OH- --->O2+2H2O+2e-

the reduction half reaction is CI2O7-->CIO2-

THE CI atoms are balanced Cl2O7--->CIO2-

8 electrons are added to balance the oxidation number CI2O7+8e- -->CIO2-

6 hydroxide ions are added to balance the charge CI2O7+8e- --->CIO2-+6OH-

The oxidation half equation is multiplied with 4 and added to the reduction half equation.

oxidation number method

total decrease in oxidation number of CI2O7 is 8

total increase in oxidation number of H2O2 IS 2

H202 AND O2 are multiplied with 4

CI2O7+4H2O2--->CIO2-+4O2

Chlorine atoms are balanced CI2O7+4H2O2--->2CIO2-+4O2

O atoms are balamced by adding 3 water molecules CI2O7+4H2O2--->2CIO2- +4O2+3H2O

H atoms are balanced by adding 2 hydroxide ions and 2 water molecules.CI2O7+4H2O2+2OH- --->CIO2- +4O2+5H2O