Question

A redox reaction is one in which:
(A) Both the substances are reduced.
(B) Both the substances are oxidised.
(C) One substance is reduced and the other is oxidised.
(D) All of the above.

Answer 1

A redox reaction is a type of reaction in which there is transfer of electrons from one of the reactants to another reactant. In other words one behaves as an oxidising agent while the other behaves as a reducing agent.

Complete step by step answer:
-First of all let us see what redox reactions are.
Any chemical reaction in which the electrons are transferred between the atoms involved as reactants is known as a redox reaction. During this reaction there is a change of oxidation state of the reacting species, the oxidation state of one gets reduced while that of the other increases. In this process there occur both the oxidation and reduction processes.
A general form of such a reaction is:
$A + B \to {A^ + } + {B^ - }$

-From this general form we can tell that the reactant A loses an electron to form ${A^ + }$, which means it gets oxidised; while B attains an electron to form ${B^ - }$, which means it gets reduced. Hence from this we can conclude that one of the reactants gets oxidised while the other gets reduced.
-Some examples of redox reaction are as follows:

1. ${H_2} + C{l_2} \to 2HCl$
2. $CaC{O_3} \to CaO + C{O_2}$
3. $CuS{O_4} + Zn \to Cu + ZnS{O_4}$
4. $4Fe + 3{O_2} \to 2F{e_2}{O_3}$, etc.

-The species which accepts electrons and undergoes reduction acts as an oxidizing agent, while the other reactant which loses electrons and undergoes oxidation will act as a reducing agent. Hence these redox reactions are broken down into 2 half cell reactions: the oxidation half-reaction and the reduction half-reaction.
-These reduction reactions can be of various types like: displacement reaction, combination reaction, decomposition reaction and the disproportionation reaction. The redox reactions are basically used in the process of electrolysis, electroplating, metal separation from the ores, steel galvanization, smelting of metal sulfides, etc.
So, the correct answer is “Option C”.

Note: A disproportionation reaction is a special type of redox reaction in which the same substance is both oxidised and reduced. For example:
$H{g_2}C{l_2} \to Hg + HgC{l_2}$
Here, mercury exists in the form of $H{g^ + }$, it gets reduced into Hg and oxidised into $H{g^{ + 2}}$.