Question

Which of the following pair of ions have equal number of unpaired electrons?

• A. \( \text{V}^{2+} \) and \( \text{Ni}^{2+} \)
• B. \( \text{Cr}^{2+} \) and \( \text{Mn}^{2+} \)
• C. \( \text{Fe}^{2+} \) and \( \text{Sc}^{2+} \)
• D. \( \text{Mn}^{3+} \) and \( \text{Fe}^{2+} \)

Hint:

The number of unpaired electrons in transition metal ions is determined by their electron configuration. For ions, electrons are removed first from the outermost orbitals. To determine the number of unpaired electrons, carefully examine the electron configuration of each ion and consider the d-block elements where unpaired electrons are more common.

Answer 1

The Correct Option is B

To determine the number of unpaired electrons, the electron configurations of the ions are presented:- V\(^2+\) (Vanadium \( Z = 23 \)): The electron configuration of \( \text{V} \) is \( [\text{Ar}] 3d^3 4s^2 \). Loss of two electrons yields \( [\text{Ar}] 3d^3 \), resulting in 3 unpaired electrons.- Ni\(^2+\) (Nickel \( Z = 28 \)): The electron configuration of \( \text{Ni} \) is \( [\text{Ar}] 3d^8 4s^2 \). Loss of two electrons yields \( [\text{Ar}] 3d^8 \), resulting in 2 unpaired electrons.- Cr\(^2+\) (Chromium \( Z = 24 \)): The electron configuration of \( \text{Cr} \) is \( [\text{Ar}] 3d^5 4s^1 \). Loss of two electrons yields \( [\text{Ar}] 3d^4 \), resulting in 4 unpaired electrons.- Mn\(^2+\) (Manganese \( Z = 25 \)): The electron configuration of \( \text{Mn} \) is \( [\text{Ar}] 3d^5 4s^2 \). Loss of two electrons yields \( [\text{Ar}] 3d^5 \), resulting in 5 unpaired electrons.- Fe\(^2+\) (Iron \( Z = 26 \)): The electron configuration of \( \text{Fe} \) is \( [\text{Ar}] 3d^6 4s^2 \). Loss of two electrons yields \( [\text{Ar}] 3d^6 \), resulting in 4 unpaired electrons.- Sc\(^2+\) (Scandium \( Z = 21 \)): The electron configuration of \( \text{Sc} \) is \( [\text{Ar}] 3d^1 4s^2 \). Loss of two electrons yields \( [\text{Ar}] 3d^1 \), resulting in 1 unpaired electron.- Mn\(^3+\) (Manganese \( Z = 25 \)): The electron configuration of \( \text{Mn} \) is \( [\text{Ar}] 3d^5 4s^2 \). Loss of three electrons yields \( [\text{Ar}] 3d^4 \), resulting in 4 unpaired electrons.- Fe\(^2+\) (Iron \( Z = 26 \)): The electron configuration for \( \text{Fe}^{2+} \) is \( [\text{Ar}] 3d^6 \), with 4 unpaired electrons, as previously determined.Comparison of unpaired electron counts:- Cr\(^2+\) has 4 unpaired electrons.- Mn\(^2+\) has 5 unpaired electrons.These do not match. Therefore, the correct pair with an equal number of unpaired electrons is not \( \text{Cr}^{2+} \) and \( \text{Mn}^{2+} \).