Answer :
Answer : The answer is none of the above.
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.
The given balanced chemical reaction is :
[tex]CuS+NO_3^-\rightarrow CuSO_4+NO_2[/tex]
The oxidation state of 'Cu' in [tex]CuS[/tex] and [tex]CuSO_4[/tex] is, (+2).
In this reaction, the oxidation state of 'S' changes from (-2) to (+6) that means 'S' lost 4 electrons and it shows oxidation and the oxidation state of 'N' changes from (+5) to (+4) that means 'N' gains 1 electron and it shows reduction. That means electrons are donated from 'S' in CuS to 'N' in [tex]NO_3^-[/tex].
The oxidation-reduction half reaction will be :
Oxidation : [tex]S^{2-}\rightarrow S^{6+}+4e^-[/tex]
Reduction : [tex]N^{5+}+1e^-\rightarrow N^{4+}[/tex]
All the given statements are correct.
Hence, the answer is none of the above.