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Step-1 Split the reaction in two half cell reaction and balance the central atom and other elements on the basis of priority of metal>non-metal>oxygen>hydrogen. Oxygen and hydrogen will be balanced by H₂O and OH^? only.

MnO₄ ¯ (aq) + 2H₂O  MnO₂ + 4HO^?

2I^?  I₂

Step-2 Cross-multiply the equation with change in oxidation number w.r.t. central

atom

MnO₄ ¯ (aq) + 2H₂O  MnO₂ + 4HO^? x 2

2I^?  I₂ x 3

Step-3 Add the equation

2MnO₄ ¯ (aq) + 4H₂O + 6I^?  2MnO₂ + 3I₂ + 8HO^?

Step- 4 Simplify the equation to get the balanced equation.

2MnO₄ ¯ (aq) + 4H₂O + 6I^?  2MnO₂ + 3I₂ + 8HO^?

^{Half reaction method}

1. Assign oxidation states to all atoms in the reactants and products. 2. Remove spectator ions from the equation, if any occur, except for those containing only H and/or O. 

3. Write two half-reactions, one for oxidation and one for reduction. If you have multiple oxidations, put them all together in one half reaction. Do the same if you have multiple reductions. 

4. Balance each half-reaction as follows: 

a. Balance all elements other than oxygen and hydrogen. 

b. Balance oxygen by adding the appropriate number of water molecules (H2O) to the side of the equation that needs more oxygen atoms. 

c. Balance hydrogen by adding the appropriate number of hydrogen ions (H+) to the side of the equation that needs more hydrogen atoms. 

d. Balance the charge by adding the appropriate number of electrons to the side of the equation with the greater overall positive charge. 

5. Multiply each half-reaction by a whole number so that the electrons lost in the oxidation half-reaction equal the number of electrons gained in the reduction half-reaction. 

6. Add the two half reactions together, keeping all of the reactants together on the left side of the reaction arrow and all of the products together on the right side of the reaction arrow. The electrons will cancel so they are not shown in the final equation. 

7. Cancel any substances that appear on both sides of the equation. Check to make sure that the equation is balanced. If you removed spectator ions before you wrote the half-reactions, put them back in and balance by inspection. 

8. If your reaction occurs in a basic solution, you must also do the following. Remove any H+ from the equation by adding an equal number of OH- ions to both sides of the equation. Remember that H+ + OH- forms H2O so you can replace the H+ and OH- that occur on the same side with an equal number of H2O. Now cancel any water molecules that appear on both sides of the equation.