Chemistry - Coordination Chemistry Question with Solution | TestHub

Option A is correct because the chelation effect dictates that complexes with multidentate ligands (like ethylenediamine, 'en') are more stable than those with monodentate ligands (like ammonia, NH₃). Therefore, $[Ni(en{)}_3{]}^{2+}$ should be MORE stable than $[Ni(N{H}_3{)}_6{]}^{2+}$.

Option C is correct. Crystal field splitting energy (CFSE) depends on the ligand. $F^{-}$ is a weak field ligand, while $H_{2}O$ is a stronger field ligand. Therefore, $[Fe(F{)}_6{]}^{3-}$ will have a LOWER crystal field splitting energy than $[Fe(H_{2}O{)}_6{]}^{3+}$.

Option B is incorrect because SCN⁻ is a weaker field ligand than CN⁻, so the complex with SCN⁻ will be less stable.

Option D is incorrect because $Co(CO{)}_4^{-}$ has 18 valence electrons (9 from Co⁻ + 8 from 4CO + 1 from the negative charge), while $Ni(CO{)}_4$ also has 18 valence electrons (10 from Ni + 8 from 4CO).

Final Answer: The final answer is $\boxed{A,C}$