Question

Which of the following is a redox reaction:
A. $2Na\left[ Ag{{\left( CN \right)}_{2}} \right]+Zn\to N{{a}_{2}}\left[ Zn{{\left( CN \right)}_{4}} \right]+2Ag$
B. $Ba{{O}_{2}}+{{H}_{2}}S{{O}_{4}}\to BaS{{O}_{4}}+{{H}_{2}}{{O}_{2}}$
C. ${{N}_{2}}{{O}_{5}}+{{H}_{2}}O\to 2HN{{O}_{3}}$
D. $AgN{{O}_{3}}+KI\to AgI+KN{{O}_{3}}$

Answer 1

Hint: As we know that a redox reaction is a type of reaction in which the transfer of electrons takes place from one of the reactants to another reactant. Or we can say that one behaves as a reducing agent, whereas another behaves as an oxidising agent.

Complete step by step answer:
- As we know that in any chemical reaction in which the electrons are transferred between the atoms that are basically involved as reactants is called a redox reaction. We can see that in oxidation loss of electrons takes place or we can say gain of oxygen takes place. Whereas, in reduction, gain of electrons takes place or we can say gain of hydrogen takes place.
- It is also found that the oxidising agent can gain electrons and itself get reduced in the reaction. Whereas, reducing agent loses electrons and gets oxidised itself.
- In the first reaction, $2Na\left[ Ag{{\left( CN \right)}_{2}} \right]+Zn\to N{{a}_{2}}\left[ Zn{{\left( CN \right)}_{4}} \right]+2Ag$, we can see that the oxidation number of Ag is changing from +2 to 0, that is it is undergoing reduction. Whereas, the oxidation number of Zn is changing from 0 to +4, that is it is undergoing Oxidation. Here we can see that both the process of oxidation and reduction is taking place.
- In the second, third and fourth reaction, we can see that no reduction or oxidation is taking place.
- Hence, we can conclude that the correct option is (a), that is the redox reaction is: $2Na\left[ Ag{{\left( CN \right)}_{2}} \right]+Zn\to N{{a}_{2}}\left[ Zn{{\left( CN \right)}_{4}} \right]+2Ag$
So the correct answer is “A”:

Note: - As we know that there is a special type of reaction called a disproportionation reaction, in which the same substance is found to both get oxidised or get reduced. For example in the reaction: $H{{g}_{2}}C{{l}_{2}}\to Hg+HgC{{l}_{2}}$
- Here, we can see that mercury is present in the form of $H{{g}^{+}}$, and it gets oxidised into $H{{g}^{2+}}$ and gets reduced into Hg.