Which of the following cannot be explained by crystal field theory?

Solution

Chemistry ma’am · 3 steps

Ligands as point charges cannot explain why neutral CO splits d orbitals more than F⁻.

1. What CFT assumes. Crystal field theory treats every ligand as a point negative charge, or a dipole, that repels the metal's d electrons. The bond is taken as purely ionic, with no sharing of electrons.
2. Where it breaks. On that picture, anions such as F⁻ and Cl⁻ should split the d orbitals the most. In the real series, neutral NH₃ and CO split them far more. That needs covalent and π-bonding effects, which CFT leaves out.

   Property	How CFT handles it	Explained by CFT?
   Order of spectrochemical series	Only measured from spectra. The point-charge model predicts the wrong order.	No
   Stability	Crystal field stabilisation energy (CFSE)	Yes
   Magnetic properties	Compares Δₒ with pairing energy, which gives high spin or low spin and the number of unpaired electrons	Yes
   Colour	d–d transition: an electron absorbs light of energy Δ and jumps to the higher set	Yes

3. So. CFT uses the spectrochemical series as an experimental input but cannot explain its order. The answer is (a).

The idea to keep. CFT explains colour, magnetism and CFSE, but its purely ionic picture cannot explain the spectrochemical series or covalent character. For those you need ligand field or MO theory.

Answer from the NTA final answer key. Solution by PrepWiser.