Explanation :
Redox reaction or Oxidation-reduction reaction : It is defined as the reaction in which the oxidation and reduction reaction takes place simultaneously.
Oxidation reaction : It is defined as the reaction in which a substance looses its electrons. In this, oxidation state of an element increases. Or we can say that in oxidation, the loss of electrons takes place.
Reduction reaction : It is defined as the reaction in which a substance gains electrons. In this, oxidation state of an element decreases. Or we can say that in reduction, the gain of electrons takes place.
<u>(a) The given chemical reaction is :</u>

The oxidation-reduction half reaction will be :
Oxidation : 
Reduction : 
In order to balance the electrons, we multiply the oxidation reaction by 3 and reduction reaction by 2 then added both equation, we get the balanced redox reaction.
The balanced chemical equation in a basic solution will be,

<u>(b) The given chemical reaction is :</u>

The oxidation-reduction half reaction will be :
Oxidation : 
Reduction : 
In order to balance the electrons, we multiply the oxidation reaction by 2 and then added both equation, we get the balanced redox reaction.
The balanced chemical equation in a basic solution will be,

<u>(c) The given chemical reaction is :</u>

The oxidation-reduction half reaction will be :
Oxidation : 
Reduction : 
The electrons in oxidation and reduction reaction are same. Now add both the equation, we get the balanced redox reaction.
The balanced chemical equation in a acidic solution will be,
