The crystal field splitting energy Δ0 depends on the strength of the ligand.
According to the spectrochemical series, the order of ligand strength is F−<H2O<en<CN−.
Thus, the order of Δ0 for the given complexes is [CrF6]3−<[Cr(H2O)6]3+<[Cr(en)3]3+<[Cr(CN)6]3−.
Matching with the given values:
[CrF6]3− has the minimum Δ0=15,060 cm−1 (B → I).
[Cr(H2O)6]3+ has Δ0=17,400 cm−1 (C → II).
[Cr(en)3]3+ has Δ0=22,300 cm−1 (D → III).
[Cr(CN)6]3− has the maximum Δ0=26,600 cm−1 (A → IV).
This corresponds to A-IV, B-I, C-II, D-III.
Answer: A-IV, B-I, C-II, D-III