Question

Which of the following statements is incorrect? 

• A. [VF₆]^3- is paramagnetic with 2 unpaired electrons.
• B. [CuCl₄]^2- is paramagnetic with 1 unpaired electron.
• C. [Co(NH₃)₆]³⁺ is diamagnetic
• D. [CoF₆]^3- is paramagnetic with 2 unpaired electrons.

Answer 1

The Correct Option is D

Let's analyze each complex and check their magnetic properties:

1. [VF₆]³⁻:  
   V³⁺ has the configuration 3d². 
   With a weak field ligand like F⁻, it forms a high-spin complex, so both electrons remain unpaired. 
   ✅ Paramagnetic with 2 unpaired electrons — Correct.
2. [CuCl₄]²⁻: 
   Cu²⁺ has the configuration 3d⁹. 
   One unpaired electron remains. 
   ✅ Paramagnetic with 1 unpaired electron — Correct.
3. [Co(NH₃)₆]³⁺: 
   Co³⁺ is 3d⁶. NH₃ is a strong field ligand, so it forms a low-spin complex. 
   All electrons are paired. 
   ✅ Diamagnetic — Correct.
4. [CoF₆]³⁻: 
   Co³⁺ is 3d⁶. F⁻ is a weak field ligand, so it forms a high-spin complex. 
   This results in 4 unpaired electrons, not 2. 
   ❌ Paramagnetic with 2 unpaired electrons — Incorrect.

Therefore, the correct answer is option (D): [CoF₆]³⁻ is paramagnetic with 2 unpaired electrons — which is incorrect because it actually has 4 unpaired electrons.