Question

For which of the following ions is the magnetic moment \( (\mu) \) the highest?

• A. \( Zn^{2+} \)
• B. \( Fe^{2+} \)
• C. \( Co^{2+} \)
• D. \( Ni^{2+} \)

Hint:

Magnetic moment rises with the number of unpaired d-electrons; count them for each ion.

Answer 1

The Correct Option is B

Step 1: Get electron configurations.
Neutral atoms lose electrons: Zn(30)\(\to\)Zn\(^{2+}\) = \(3d^{10}\); Fe(26)\(\to\)Fe\(^{2+}\) = \(3d^{6}\); Co(27)\(\to\)Co\(^{2+}\) = \(3d^{7}\); Ni(28)\(\to\)Ni\(^{2+}\) = \(3d^{8}\).

Step 2: Distribute in five d-orbitals (Hund's rule).
\(d^{10}\): 0 unpaired; \(d^{6}\): 4 unpaired; \(d^{7}\): 3 unpaired; \(d^{8}\): 2 unpaired.

Step 3: Highest unpaired count gives highest moment.
\(Fe^{2+}\) with 4 unpaired electrons wins, \(\mu = \sqrt{n(n+2)} = \sqrt{24} \approx 4.9\) BM.
\[\boxed{Fe^{2+}\ \text{(option ii)}}\]