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The correct order of [FeF 6 ] 3 – , [CoF 6 ] 3 – , [Ni(CO) 4 ] and [Ni (CN) 4 ] 2 – complex species based on the number of unpaired electrons present is

1. [FeF 6 ] 3 – > [CoF 6 ] 3 – > [Ni(CN) 4 ] 2 – = [Ni(CO) 4 ]
2. [Ni(CN) 4 ] 2 – > [FeF 6 ] 3 – > [CoF 6 ] 3 – > [Ni(CO) 4 ]
3. [CoF 6 ] 3 – > [FeF 6 ] 3 – > [Ni(CO) 4 ] > [Ni(CN) 4 ] 2 –
4. [FeF 6 ] 3 – > [CoF 6 ] 3 – > [Ni(CN) 4 ] 2 – > [Ni(CO) 4 ]

Correct answer: [FeF 6 ] 3 – > [CoF 6 ] 3 – > [Ni(CN) 4 ] 2 – = [Ni(CO) 4 ]

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