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

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.