Question

Directions: Each set of lettered choices below refers to the numbered statements immediately following it. Select the one lettered choice that best fits each statement. A choice may be used once, more than once, or not at all in each set. The following questions refer to the reactions represented below. (A) H2SeO4(aq) + 2 Cl-(aq) + 2 H+(aq) → H2SeO3(aq) + Cl2(g) + H2O(l) (B) S8(s) + 8 O2(g) → 8 SO2(g) (C) 3 Br2(aq) + 6 OH-(aq) → 5 Br-(aq) + BrO3-(aq) + 3 H2O(l) (D) Ca2+(aq) + SO42-(aq) → CaSO4(s) (E) PtCl4(s) + 2 Cl-(aq) → PtCl62-(aq) A reaction in which the same reactant undergoes both oxidation and reduction

Answer 1

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,

$H_2SeO_4(aq)+2Cl^-(aq)+2H^+(aq)\rightarrow H_2SeO_3(aq)+Cl_2(g)+H_2O(l)$

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,

$S_8(s)+8O_2(g)\rightarrow 8SO_2(g)$

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,

$3Br_2(aq)+6OH^-(aq)\rightarrow 5Br^-(aq)+BrO_3^-(aq)+3H_2O(l)$

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,

$Ca^{2+}(aq)+SO_4^{2-}(aq)\rightarrow CaSO_4(s)$

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,

$PtCl_4(s)+2Cl^-(aq)\rightarrow PtCl_6^{2-}(aq)$

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.