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Chemistry · Coordination Compounds

JEE Main 2025 — 4 April, Evening Shift — Question 9

The correct order of [FeF6]3−,[CoF6]3−,[Ni(CO)4]\left[\mathrm{FeF}_{6}\right]^{3-},\left[\mathrm{CoF}_{6}\right]^{3-},\left[\mathrm{Ni}(\mathrm{CO})_{4}\right] and [Ni(CN)4]2−\left[\mathrm{Ni}(\mathrm{CN})_{4}\right]^{2-} complex species based on

the number of unpaired electrons present is

  1. Option A:

    [FeF6]3−>[CoF6]3−>[Ni(CN)4]2−=[Ni(CO)4]\left[\mathrm{FeF}_{6}\right]^{3-}>\left[\mathrm{CoF}_{6}\right]^{3-}>\left[\mathrm{Ni}(\mathrm{CN})_{4}\right]^{2-}=\left[\mathrm{Ni}(\mathrm{CO})_{4}\right]

    Correct
  2. Option B:

    [Ni(CN)4]2−>[FeF6]3−>[CoF6]3−>[Ni(CO)4]\left[\mathrm{Ni}(\mathrm{CN})_{4}\right]^{2-}>\left[\mathrm{FeF}_{6}\right]^{3-}>\left[\mathrm{CoF}_{6}\right]^{3-}>\left[\mathrm{Ni}(\mathrm{CO})_{4}\right]

  3. Option C:

    [CoF6]3−>[FeF6]3−>[Ni(CO)4]>[Ni(CN)4]2−\left[\mathrm{CoF}_{6}\right]^{3-}>\left[\mathrm{FeF}_{6}\right]^{3-}>\left[\mathrm{Ni}(\mathrm{CO})_{4}\right]>\left[\mathrm{Ni}(\mathrm{CN})_{4}\right]^{2-}

  4. Option D:

    [FeF6]3−>[CoF6]3−>[Ni(CN)4]2−>[Ni(CO)4]\left[\mathrm{FeF}_{6}\right]^{3-}>\left[\mathrm{CoF}_{6}\right]^{3-}>\left[\mathrm{Ni}(\mathrm{CN})_{4}\right]^{2-}>\left[\mathrm{Ni}(\mathrm{CO})_{4}\right]

Answer: A

Step-by-step solution

[FeF6]3−\left[\mathrm{FeF}_{6}\right]^{3-}

Fe3+⇒t2 g3eg2\mathrm{Fe}^{3+} \Rightarrow \mathrm{t}_{2 \mathrm{~g}}^{3} \mathrm{e}_{\mathrm{g}}^{2}

No. of unpaired electron =5=5

[CoF6]3+\left[\mathrm{CoF}_{6}\right]^{3+}

Co3+⇒t2 g4eg2\mathrm{Co}^{3+} \Rightarrow \mathrm{t}_{2 \mathrm{~g}}^{4} \mathrm{e}_{\mathrm{g}}^{2}

No. of unpaired electron =4=4

Ni(CO)4⇒Ni0⇒3d104 s0\mathrm{Ni}(\mathrm{CO})_{4} \Rightarrow \mathrm{Ni}^{0} \Rightarrow 3 d^{10} 4 \mathrm{~s}^{0} in presence of CO ligand

No. of unpaired electron =0=0

[Ni(CN)E2−\left[\mathrm{Ni}(\mathrm{CN}) \mathrm{E}^{2-}\right.

Ni4+⇒t2 g6eg0\mathrm{Ni}^{4+} \Rightarrow \mathrm{t}_{2 \mathrm{~g}}^{6} \mathrm{e}_{\mathrm{g}}^{0}

No. of unpaired electron =0=0

Answer key and solution verified before publishing.

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Exam
JEE Main 2025
Paper
4 April, Evening Shift
Subject
Chemistry
Chapter
Coordination Compounds
Topic
Properties and importance of Coordination Complexes

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