Q.Assertion (A): Redox couple is the combination of oxidised and reduced form of a substance involved in an oxidation or reduction half cell.
Reason (R): In the representation E⊖(Fe^3+/Fe^2+) and E⊖(Cu^2+/Cu), Fe^3+/Fe^2+ and Cu^2+/Cu are redox couples.

The key concept here is the redox couple, which is fundamental to understanding electrode potentials and electrochemical cells.

1. Assertion (A) Analysis: A redox couple is indeed defined as the combination of the oxidised and reduced forms of a substance involved in a half-cell reaction. For example, in the reduction half-reaction $M^{n+} + ne^- \rightarrow M$, $M^{n+}$ is the oxidised form and $M$ is the reduced form, forming the redox couple $M^{n+}/M$. Thus, Assertion (A) is true.
2. Reason (R) Analysis: The representations $E^\ominus(Fe^{3+}/Fe^{2+})$ and $E^\ominus(Cu^{2+}/Cu)$ correctly denote the standard electrode potentials for the respective redox couples. In $Fe^{3+}/Fe^{2+}$, $Fe^{3+}$ is the oxidised form and $Fe^{2+}$ is the reduced form. In $Cu^{2+}/Cu$, $Cu^{2+}$ is the oxidised form and $Cu$ is the reduced form. These are valid examples of redox couples. Thus, Reason (R) is true. …

In electrochemistry, reactions are often broken down into two half-reactions: one involving oxidation and the other reduction. Each of these half-reactions involves a pair of species that are interconvertible by the gain or loss of electrons. This pair is fundamental to understanding how electron transfer occurs and is termed a 'redox couple'.

Understanding Redox Couples

A redox couple consists of the oxidised and reduced forms of a particular substance. These two forms are related by an electron transfer process.

• The oxidised form is the species that has lost electrons (or has a higher oxidation state).
• The reduced form is the species that has gained electrons (or has a lower oxidation state).

For example, in the half-reaction $\text{Zn}^{2+} + 2e^- \rightleftharpoons \text{Zn}$, $\text{Zn}^{2+}$ is the oxidised form and $\text{Zn}$ is the reduced form. Together, they constitute the $\text{Zn}^{2+}/\text{Zn}$ redox couple. The notation for a redox couple is typically (oxidised form / reduced form).

Standard electrode potentials ($E^\ominus$) are always associated with a specific redox couple, indicating the tendency of the oxidised form to get reduced.

1. Evaluate Assertion (A):

   The assertion states: "Redox couple is the combination of oxidised and reduced form of a substance involved in an oxidation or reduction half cell."

   This statement accurately defines a redox couple. As discussed, a redox couple is precisely this pair of species, differing by the number of electrons, that participates in a half-reaction.

   Therefore, Assertion (A) is true.

2. Evaluate Reason (R):

   The reason states: "In the representation $E^\ominus(\text{Fe}^{3+}/\text{Fe}^{2+})$ and $E^\ominus(\text{Cu}^{2+}/\text{Cu})$, $\text{Fe}^{3+}/\text{Fe}^{2+}$ and $\text{Cu}^{2+}/\text{Cu}$ are redox couples."

   Let's examine the given examples:

   • For $\text{Fe}^{3+}/\text{Fe}^{2+}$: $\text{Fe}^{3+}$ is the oxidised form (higher oxidation state) and $\text{Fe}^{2+}$ is the reduced form (lower oxidation state). They are interconvertible via the reaction $\text{Fe}^{3+} + e^- \rightleftharpoons \text{Fe}^{2+}$. This is a valid redox couple. …