Question

Identify the correct statements from the following
A. $[Fe(C_2O_4)_3]^{3-}$ is the most stable complex among $[Fe(OH)_6]^{3-}$, $[Fe(C_2O_4)_3]^{3-}$ and $[Fe(SCN)_6]^{3-}$
B. The stability of $[Cu(NH_3)_4]^{2+}$ is greater than that of $[Cu(en)_2]^{2+}$
C. The hybridization of Fe in $K_4[Fe(CN)_6]$ is $d^2sp^3$
D. $[Fe(NO_2)_3Cl_3]^{3-}$ exhibits linkage isomerism
E. $NO_2^-$ and $SCN^-$ ligands are NOT ambidentate ligands
Choose the correct answer from the options given below :

• A. A, B, C, D and E
• B. B, C and D only
• C. A, C and D only
• D. A, C and E only

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
This question evaluates multiple concepts in coordination chemistry, including complex stability (chelate effect), hybridization (VBT/CFT), and types of isomerism/ligands. 
Step 2: Detailed Explanation: 
Statement A: Oxalate ($C_2O_4^{2-}$) is a chelating ligand, whereas $OH^-$ and $SCN^-$ are monodentate. Chelating complexes are significantly more stable than non-chelating ones due to the chelate effect. Thus, A is True. 
Statement B: 'en' (ethylenediamine) is a bidentate chelating ligand, while $NH_3$ is monodentate. According to the chelate effect, $[Cu(en)_2]^{2+}$ is more stable than $[Cu(NH_3)_4]^{2+}$. Thus, B is False. 
Statement C: In $K_4[Fe(CN)_6]$, iron is in the $+2$ oxidation state ($d^6$). $CN^-$ is a strong field ligand, causing electrons to pair up in the $t_{2g}$ orbitals. This leaves two empty $3d$ orbitals for hybridization. Thus, it undergoes $d^2sp^3$ hybridization. Thus, C is True. 
Statement D: $NO_2^-$ is an ambidentate ligand (it can bind through N or O). Any complex containing an ambidentate ligand can exhibit linkage isomerism. Thus, D is True. 
Statement E: $NO_2^-$ and $SCN^-$ are classic examples of ambidentate ligands because they have more than one potential donor atom. Thus, E is False. 
Step 3: Final Answer: 
Statements A, C, and D are correct.