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JEE MainChemistryCoordination Compounds

Which of the following sets contains ONLY diamagnetic complexes?

Options

  1. A[ Fe ( CN )₆ ]³⁻ , [ CoF ₆ ]³⁻ , [ Co ( H ₂ O )₆ ]²⁺
  2. B[ Fe ( CN )₆ ]⁴⁻ , [ Co ( NH ₃)₆ ]³⁺ , [ Ni ( CN )₄ ]²⁻
  3. C[ Mn ( CN )₆ ]³⁻ , [ PtCl ₄ ]²⁻ , [ Ni ( H ₂ O )₆ ]²⁺
  4. D[ Co ( C ₂ O ₄)₃ ]³⁻ , [ Ni ( NH ₃)₆ ]²⁺ , [ Cr ( NH ₃)₆ ]³⁺

Correct answer

B. [ Fe ( CN )₆ ]⁴⁻ , [ Co ( NH ₃)₆ ]³⁺ , [ Ni ( CN )₄ ]²⁻

Step-by-step solution

For a complex to be diamagnetic, it must have zero unpaired electrons. Evaluating the correct set: - [ Fe ( CN )₆ ]⁴⁻ : Fe(II) has a 3 d ⁶ configuration. CN ⁻ is a strong field ligand, resulting in pairing of all electrons ( t _ 2 g ⁶ e _ g ⁰ ). It is diamagnetic. - [ Co ( NH ₃)₆ ]³⁺ : Co(III) has a 3 d ⁶ configuration. NH ₃ acts as a strong field ligand for Co(III), resulting in t _ 2 g ⁶ e _ g ⁰ . It is diamagnetic. - [ Ni ( CN )₄ ]²⁻ : Ni(II) has a 3 d ⁸ configuration. CN ⁻ is a strong field ligand, resulting in

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