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In which of the following order the given complex ions are arranged correctly with respect to their decreasing spin only magnetic moment? (i) [FeF6]3− (ii) [Co(NH3)6]3+ (iii) [NiCl4]2− (iv) [Cu(NH3)4]2+

1. (i) > (iii) > (iv) > (ii)
2. (ii) > (iii) > (i) > (iv)
3. (iii) > (iv) > (ii) > (i)
4. (ii) > (i) > (iii) > (iv)

Correct answer: (ii) > (iii) > (i) > (iv)

Solution

The correct order reflects the spin-only magnetic moments based on the number of unpaired electrons in each complex. [Co(NH3)6]3+ has the highest number of unpaired electrons due to its high-spin state, followed by [NiCl4]2−, which also has unpaired electrons, while [FeF6]3− and [Cu(NH3)4]2+ have fewer unpaired electrons, resulting in lower magnetic moments.

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