Verified Solution • 2025–26 Session moderate

QJEEM23Cha40c: JEE Main 2023 Chemistry - Class 12 JEEM23Cha40c Solution: The correct order of the number of unpaired electrons in the…

The correct order of the number of unpaired electrons in the given complexes is

A. [Fe(CN)6]3−\left[\mathrm{Fe}(\mathrm{CN})_{6}\right]^{3-}

B. [FeF6]3−\left[\mathrm{Fe} \mathrm{F}_{6}\right]^{3-}

C. [CoF6]3−\left[\mathrm{CoF}_{6}\right]^{3-}

D. [Cr (oxalate)3]3−\left.[\mathrm{Cr} \text { (oxalate})_{3}\right]^{3-}

E. [Ni(CO)4]\left[\mathrm{Ni}(\mathrm{CO})_{4}\right]

Choose the correct answer from the options given below:

Multiple Choice Options

  • A E < A < B < D < C
  • B A < E < D < C < B
  • C A < E < C < B < D
  • D E < A < D < C < B

Step-by-Step Verified Solution

The number of unpaired electrons in a complex can be determined by the oxidation state of the central metal atom and the ligand field splitting energy. In general, a complex with a high-spin configuration will have more unpaired electrons than a complex with a low-spin configuration.

In the given complexes, the oxidation states of the central metal atoms are:

  • Fe(II) in [Fe(CN)6]3-

  • Fe(III) in [FeF6]3-

  • Co(III) in [CoF6]3-

  • Cr(III) in [Cr(ox)3]3-

  • Ni(0) in [Ni(CO)4]

The ligand field splitting energy of a complex depends on the type of ligand. In general, ligands that are strong field ligands will split the d orbitals more than ligands that are weak field ligands.

The following table shows the number of unpaired electrons in each complex :

Complex Oxidation state Ligand field splitting energy Number of unpaired electrons
[Fe(CN)6]3- Fe(II) Low-spin 1
[FeF6]3- Fe(III) High-spin 5
[CoF6]3- Co(III) High-spin 4
[Cr(ox)3]3- Cr(III) High-spin 3
[Ni(CO)4] Ni(0) None 0

Therefore, the correct order of the number of unpaired electrons in the given complexes is :

E < A < D < C < B

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