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Consider the following complex ions, P, Q and R. P = [FeF₆]³⁻ = (IV(H₂O)₆]³⁺ and R = [Fe(H₂O)₆]²⁺ The correct order of the complex ions, according to their spin-only magnetic moment values (in B.M.) is -

1. R < Q < P
2. Q < R < P
3. R < P < Q
4. Q < P < R

Correct answer: Q < R < P

Solution

The spin-only magnetic moment depends on the number of unpaired electrons. The order Q < R < P is based on the increasing number of unpaired electrons in the complexes.

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