Question

The correct order of magnetic moments (spin only values in B.M.) is: (Atomic nos.: Mn = 25, Fe = 26, Co = 27)

• A. \([\text{Fe(CN)}_6]^{4-} > [\text{MnCl}_4]^{2-} > [\text{CoCl}_4]^{2-}\)
• B. \([\text{MnCl}_4]^{2-} > [\text{Fe(CN)}_6]^{4-} > [\text{CoCl}_4]^{2-}\)
• C. \([\text{MnCl}_4]^{2-} > [\text{CoCl}_4]^{2-} > [\text{Fe(CN)}_6]^{4-}\)
• D. \([\text{Fe(CN)}_6]^{4-} > [\text{CoCl}_4]^{2-} > [\text{MnCl}_4]^{2-}\)

Hint:

Strong ligands cause pairing and reduce magnetic moment.

Answer 1

The Correct Option is C

Step 1: \([\text{MnCl}_4]^{2-}\): Mn\(^{2+}\), high spin \(d^5\) → 5 unpaired electrons.
Step 2: \([\text{CoCl}_4]^{2-}\): Co\(^{2+}\), high spin \(d^7\) → 3 unpaired electrons.
Step 3: \([\text{Fe(CN)}_6]^{4-}\): Fe\(^{2+}\), low spin \(d^6\) → 0 unpaired electrons.