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Among the ions Sc³+, Ti³+, V³+, Cr³+, Mn³+, Fe³+, Co³+ and Ni²+, how many can form BOTH high-spin and low-spin octahedral complexes?

1. 3
2. 4
3. 5
4. 2

Correct answer: 4

Solution

Mn³+ (d4), Fe³+ (d5), Co³+ (d6) and Ni²+ (d8 -> note); the ones with d4-d7 (Mn³+ d4, Fe³+ d5, Co³+ d6, and Cr³+ is d3 no) give both spin states, totalling 4.

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