Question

Identify the complex ion/s with the least spin only magnetic moment (in BM).
I) [Fe(CN)$_6$]$^{3-}$
II) [Co(CN)$_6$]$^{3-}$
III) [Mn(CN)$_6$]$^{4-}$
IV) [Fe(CN)$_6$]$^{4-}$

• A. II \& IV only
• B. I only
• C. III only
• D. I \& III only

Hint:

CN$^-$ is a strong field ligand; it promotes low spin configuration with fewer unpaired electrons.

Answer 1

The Correct Option is A

Strong field CN$^-$ ligand causes pairing of electrons in low-spin complexes. Among the given, Co$^{3+}$ in II and Fe$^{2+}$ in IV form low-spin, diamagnetic or nearly diamagnetic complexes.