Identify the correct statements from the following A....

Statement A is correct. The oxalate ion ($C_2O_4^{2-}$) is a bidentate ligand and forms chelate rings with the central metal ion. Due to the chelate effect, $[Fe(C_2O_4)_3]^{3-}$ is more stable than complexes formed by monodentate ligands like $[Fe(OH)_6]^{3-}$ and $[Fe(SCN)_6]^{3-}$.

Statement B is incorrect. Ethylenediamine (en) is a bidentate ligand and forms chelate rings, whereas $NH_3$ is a monodentate ligand. Therefore, $[Cu(en)_2]^{2+}$ is more stable than $[Cu(NH_3)_4]^{2+}$ due to the chelate effect.

Statement C is correct. In $K_4[Fe(CN)_6]$, the oxidation state of Fe is $+2$, which corresponds to a $3d^6$ configuration. Since $CN^-$ is a strong field ligand, it causes the pairing of electrons in the $3d$ orbitals, leaving two inner $3d$ orbitals empty. Thus, the hybridization is $d^2sp^3$.

Statement D is correct. The $NO_2^-$ ligand is an ambidentate ligand, meaning it can coordinate to the metal center through either the nitrogen atom or the oxygen atom. Therefore, $[Fe(NO_2)_3Cl_3]^{3-}$ can exhibit linkage isomerism.

Statement E is incorrect. Both $NO_2^-$ and $SCN^-$ are ambidentate ligands. $NO_2^-$ can bind through N or O, and $SCN^-$ can bind through S or N.

Therefore, the correct statements are A, C, and D.

Answer: A, C and D only