Given below are two statements :
Statement (I) : In octahedral complexes, when Δ₀<P high spin complexes are formed. When Δ₀>P low spin complexes are formed.
Statement (II) : In tetrahedral complexes because of Δₜ < P, low spin complexes are rarely formed.
In the light of the above statements, choose the most appropriate answer from the options given below :

Solution

Chemistry ma’am · 4 steps

It is a contest between Δ and pairing energy P: the electron takes whichever costs less.

1. The choice. In a d⁴ to d⁷ ion, the next electron can pair up in a lower orbital, which costs the pairing energy P. Or it can go up to a higher orbital, which costs Δ. The electron takes the cheaper route.
2. Octahedral case. If Δₒ < P, going up is cheaper, so the electrons stay unpaired and the complex is high spin. If Δₒ > P, pairing is cheaper, so the complex is low spin. Statement I is correct.
3. Tetrahedral case. A tetrahedral complex has only 4 ligands, and none of them point straight at the d orbitals, so Δₜ ≈ 4/9Δₒ. This is almost always smaller than P, so pairing rarely wins and low spin tetrahedral complexes are rarely formed. Statement II is correct.
4. So. Both statements are correct, which is option (d).

The idea to keep. Compare Δ with P: if Δ > P the complex is low spin, and if Δ < P it is high spin. Since Δₜ ≈ 4/9Δₒ is small, tetrahedral complexes are almost always high spin.

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