Answer : The only reaction (C) that shows that the same reactant undergoes both oxidation and reduction.
Explanation :
Disproportionation reaction : It is defined as the reaction in which the same reactant undergoes both oxidation and reduction reaction. It is a redox reaction.
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.
(A) The given balanced reaction is,
This reaction is a redox reaction but not disproportionation reaction because in this reaction there are two reactants in which chlorine shows oxidation and selenium shows reduction.
(B) The given balanced reaction is,
This reaction is a redox reaction but not disproportionation reaction because in this reaction there are two reactants in which sulfur shows oxidation and oxygen shows reduction.
(C) The given balanced reaction is,
This reaction is a disproportionation reaction because in this reaction only one reactant bromine that shows both oxidation and reduction reaction.
(D) The given balanced reaction is,
This reaction is a combination reaction in which the two reactant react to give a single product. There is no changes in the oxidation state of calcium and sulfate.
(E) The given balanced reaction is,
This reaction is a combination reaction in which the two reactant react to give a single product. There is no changes in the oxidation state of platinum and chlorine.
Hence, the only reaction (C) that shows that the same reactant undergoes both oxidation and reduction.
