Question

Which of the following chemical equations show(s) oxidation-reduction reactions?1. Mg(s) + I2(aq) --> MgI2(s)2. Pb(ClO4)2(aq) + 2 KI(aq) --> PbI2(s) + 2 KClO4(aq)3. Fe2O3(s) + 3 CO(g) --> 2 Fe(s) + 3 CO2(g)1 only2 only1 and 21 and 32 and 3

Answer 1

Answer : The correct option is, 1 and 3

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.

(1) The given balanced chemical reaction is :

$Mg(s)+I_2(aq)\rightarrow MgI_2(s)$

The oxidation-reduction half reaction will be :

Oxidation : $Mg\rightarrow Mg^{2+}+2e^-$

Reduction : $I_2+2e^-\rightarrow 2I^-$

In this reaction, the oxidation state of 'Mg' changes from (0) to (+2) that means Mg lost 2 electrons and it shows oxidation and the oxidation state of 'I' changes from (0) to (-2) that means 'I' gains 2 electrons and it shows reduction.

(2) The given balanced chemical reaction is :

$Pb(ClO_4)_2(aq)+2KI(aq)\rightarrow PbI_2(s)+2KClO_4(aq)$

In this reaction does not shows oxidation reduction reaction. This reaction shows double displacements and in this reaction the oxidation state of lead, iodine, potassium and chlorate does not change.

(3) The given balanced chemical reaction is :

$Fe_2O_3(s)+3CO(g)\rightarrow 2Fe(s)+3CO_2(g)$

The oxidation-reduction half reaction will be :

Oxidation : $C^{2+}\rightarrow C^{4+}+2e^-$

Reduction : $Fe^{3+}+3e^-\rightarrow Fe$

In this reaction, the oxidation state of 'C' changes from (+2) to (+4) that means C lost 2 electrons and it shows oxidation and the oxidation state of 'Fe' changes from (+3) to (0) that means 'Fe' gains 3 electrons and it shows reduction.

Hence, the chemical equations show(s) oxidation-reduction reactions are, 1 and 3.