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For cobalt (atomic number 27), which of the following octahedral complexes is expected to have the largest value of Δo?

1. [Co(CN)6]3−
2. [Co(C2O4)3]3−
3. [Co(H2O)6]3+
4. [Co(NH3)6]3+

Correct answer: [Co(CN)6]3−

Solution

The complex [Co(CN)6]3− has the largest value of Δo because cyanide (CN−) is a strong field ligand that causes greater splitting of the d-orbitals compared to the other ligands listed, leading to a higher energy difference between the split d-orbitals.

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