Question

Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R).
Assertion (A): In aqueous solutions \( \text{Cr}^{2+} \) is reducing while \( \text{Mn}^{3+} \) is oxidising in nature.
Reason (R): Extra stability to half-filled electronic configuration is observed than incompletely filled electronic configuration.
In the light of the above statement, choose the most appropriate answer from the options given below:

• A. Both (A) and (R) are true and (R) is the correct explanation of (A)
• B. Both (A) and (R) are true but (R) is not the correct explanation of (A)
• C. (A) is false but (R) is true
• D. (A) is true but (R) is false

Answer 1

The Correct Option is A

Let's analyze the assertion and reason given in the question: 

1. Assertion (A): In aqueous solutions, \(\text{Cr}^{2+}\) is reducing while \(\text{Mn}^{3+}\) is oxidising in nature.
2. Reason (R): Extra stability to half-filled electronic configuration is observed than incompletely filled electronic configuration.
3. Both \(\text{Cr}^{2+}\) and \(\text{Mn}^{3+}\) are transition metal ions. Their behavior in redox reactions is influenced by their electronic configurations.
4. \(\text{Cr}^{2+}\) has the electronic configuration of \([ \text{Ar} ] \,3d^4\). It tends to lose one electron to form the more stable \([ \text{Ar} ] \,3d^5\) configuration, where all five 3d subshells are half-filled. Therefore, \(\text{Cr}^{2+}\) acts as a reducing agent.
5. \(\text{Mn}^{3+}\) has the electronic configuration of \([ \text{Ar} ] \,3d^4\). By gaining an electron, it attains the stable half-filled configuration \([ \text{Ar} ] \,3d^5\). Hence, \(\text{Mn}^{3+}\) acts as an oxidizing agent.
6. The reason provided is that the stability of the half-filled 3d subshell is significant in determining the redox behavior of these ions.

From the analysis above, we can conclude:

• Both the assertion and reason are true.
• The reason correctly explains why the assertion is true (i.e., the redox behavior of these ions is indeed due to the stability of their electronic configurations).

Therefore, the most appropriate answer is: Both (A) and (R) are true and (R) is the correct explanation of (A).

Answer 2

Explanation of Assertion (A):
In aqueous solutions, $\text{Cr}^{2+}$ acts as a reducing agent and is oxidised to $\text{Cr}^{3+}$. This is because $\text{Cr}^{3+}$ has a stable $d^3$ electronic configuration. Conversely, $\text{Mn}^{3+}$ acts as an oxidising agent and is reduced to $\text{Mn}^{2+}$, which has a stable half-filled $d^5$ electronic configuration.
Explanation of Reason (R):
The half-filled electronic configuration provides extra stability due to symmetrical distribution of electrons and exchange energy. This explains why $\text{Cr}^{3+}$ and $\text{Mn}^{2+}$ are more stable compared to their respective other oxidation states.
Conclusion:
Both Assertion (A) and Reason (R) are true. The reason given (R) correctly explains why $\text{Cr}^{2+}$ is reducing and $\text{Mn}^{3+}$ is oxidising, as it is related to the stability of the resulting electronic configurations.