Equation representing the process by which standard reduction potential of zinc can be defined is?
(A) $ Z{n^{2 + }}(s) + 2{e^ - } \to Zn $
(B) $ Zn(g) \to Z{n^{2 + }}(g) + 2{e^ - } $
(C) $ Z{n^{2 + }}(g) + 2{e^ - } \to Zn $
(D) $ Z{n^{2 + }}_{(aq)} + 2{e^ - } \to Zn $

Hint: Redox reaction is composed of two reactions i.e. reduction and oxidation reactions in an electrochemical cell. Similarly redox potential consists of two terms – reduction potential and the oxidation potential.

Complete answer:
To answer this question, first we need to understand the terms reduction potential and the oxidation potential.
So, the oxidation potential is the measure of the tendency of an ion to lose electrons to an electrode in an electrochemical cell. The atom itself gets oxidized by losing electrons.
And the Reduction potential of the ion can be defined as the measure of its tendency to gain electrons from an electrode in a cell. So, in this process the ion itself gets reduced and oxidized the other atom.
So, in our question, we are asked the equation describing the reduction potential of zinc. So, we have to choose the equation in which the zinc is reduced.
So, looking at our given options we find the correct equation is:
 $ Z{n^{2 + }}_{(aq)} + 2{e^ - } \to Zn $
In this, the zinc is reduced from the $ + 2 $ oxidation state to $ 0 $ .
We can also write the proper equation as:
 $ Z{n^{2 + }}_{(aq)} + 2{e^ - } \to Zn...........{E_{reduction}} = - 0.76 $
Here, the correct reduction potential of zinc is mentioned.
Therefore, the correct option is D.

Note:
Reduction potential is described as the negative of the oxidation potential and also it is a useful quantity in laboratories. Reduction potential or redox potential helps in the chemical reactions to know the directionality of the reaction.Also, one interesting fact to note is that the fluorine gas has the highest reduction potential being the most powerful oxidising agent.