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: Formula used.
Spin-only magnetic moment \( \mu = \sqrt{n(n+2)} \) BM, where \(n\) is the number of unpaired electrons. More unpaired electrons means higher \( \mu \).

Step 2: Find d-electron count and unpaired electrons.
\( Zn^{2+} \): \(3d^{10}\), \(n = 0\).
\( Fe^{2+} \): \(3d^{6}\), \(n = 4\).
\( Co^{2+} \): \(3d^{7}\), \(n = 3\).
\( Ni^{2+} \): \(3d^{8}\), \(n = 2\).

Step 3: Compare.
\( Fe^{2+} \) has the maximum unpaired electrons (4), so \( \mu = \sqrt{4(4+2)} = \sqrt{24} \approx 4.90 \) BM, the highest.

Conclusion: Option (ii), \( Fe^{2+} \).
\[\boxed{Fe^{2+},\ n = 4}\]