Question

Which reaction represents oxidation-reduction reaction?
A. $3{{{O}}_{2\left( {{g}} \right)}} \rightleftharpoons 2{{{O}}_{3\left( {{g}} \right)}}$
B. ${{O}}{{{H}}^ - } + {{{H}}_3}{{{O}}^ + } \rightleftharpoons {{{H}}_2}{{O}}$
C. ${{BaC}}{{{l}}_2}.2{{{H}}_2}{{{O}}_{\left( {{s}} \right)}}\xrightarrow{\Delta }{{BaC}}{{{l}}_{2\left( {{s}} \right)}} + 2{{{H}}_2}{{{O}}_{\left( {{g}} \right)}}$
D. ${{C}}{{{a}}^{2 + }} + {{C}}{{{O}}_3}^{2 - } \to {{CaC}}{{{O}}_{3\left( {{s}} \right)}}$
E. ${{Fe}} + {{C}}{{{u}}^{2 + }} \rightleftharpoons {{F}}{{{e}}^{2 + }} + {{Cu}}$

Answer 1

Oxidation-reduction reaction is also known as redox reaction. When the atoms change their oxidation state in a chemical reaction, then it is called redox reaction. It involves transfer of electrons between atoms or molecules or ions.

Complete step by step answer:
The redox reaction is a combination of oxidation and reduction reaction. When the oxidation number or state is increased, it defines the oxidation reaction. When the oxidation number is decreased, it defines the reduction reaction. Electrons are lost during oxidation while electrons are gained during reduction.
In a redox reaction, there will be an oxidizing agent and reducing agent. Oxidizing agent has the ability to gain electrons and oxidize other species. The reducing agent has the ability to give out electrons and reduce other species. Now let’s focus on the options.
A. In the given option, there is no change in the oxidation state since both the molecules do not have charge and thus it has zero oxidation state.
B. In this reaction, there is no transfer of electrons occurred. Thus it is not a redox reaction.
C. This reaction is typically a dehydration reaction, not a redox reaction.
D. This is a precipitation reaction, not a redox reaction.
E. This is a redox reaction. ${{Fe}}$ has a zero oxidation state, which changed to $+ 2$ oxidation state. While ${{C}}{{{u}}^{2 + }}$ changed its oxidation state $+ 2$ to zero. ${{Fe}}$ is the reducing agent and ${{C}}{{{u}}^{2 + }}$ is the oxidizing agent. There is a transfer of two electrons occurred in the reaction.

Hence the correct option is E.

Note: An important thing to remember the definition of oxidation and reduction is OILRIG. This means that Oxidation Is Loss and Reduction Is Gain of electrons. In some reactions, one atom or species or molecule is oxidized and reduced. This type of reaction is called disproportionation reaction.