Which of the following complexes exhibits the highest crystal field splitting energy?

Solution

1. Crystal field splitting energy ${\Delta }_o$ increases as we move down a group for the same oxidation state.
2. The metal ions are ${\text{Co}}^{3+}$, ${\text{Rh}}^{3+}$, and ${\text{Ir}}^{3+}$, all in the same group.
3. The order of splitting is ${\text{Co}}^{3+}<{\text{Rh}}^{3+}<{\text{Ir}}^{3+}$.
4. Therefore, ${\text{[Ir(NH}}_3{)}_6{\text{]}}^{3+}$ has the largest ${\Delta }_o$.
5. Hence the answer is (D).