Chemistry - Coordination Chemistry Question with Solution | TestHub

The correct options are (B) $[Fe(CN{)}_6]$³⁻ and (C) $[Co(CN{)}_6]$⁴⁻.

(B) $[Fe(CN{)}_6]$³⁻: Fe³⁺ has a $3d^5$ configuration. CN⁻ is a strong field ligand, forcing pairing to form a low-spin complex ($t_{2g}^5{e}_g^0$) with one unpaired electron (paramagnetic).

(C) $[Co(CN{)}_6]$⁴⁻: Co²⁺ has a $3d^7$ configuration. CN⁻ creates a strong field leading to a low-spin configuration ($t_{2g}^6{e}_g^1$) with one unpaired electron (paramagnetic).

(A) is diamagnetic ($d^6$, low spin due to high $+4$ oxidation state), and (D) is a $d^3$ system where high/low spin distinction does not exist.