Question

Match List l with List ll.

List I Coordination Complex	List II Number of unpaired electrons
(I) [Cr(CN)6]3-	(a) 0
(II) [Fe(H2O)6]2+	(b) 3
(III) [Co(NH3)6]3+	(c) 2
(IV) [Ni(NH3)6]2+	(d) 4

Choose the correct answer from the options given below:

• A. A-II, B-IV, C-I, D-III
• B. A-III, B-IV, C-I, D-II
• C. A-II, B-I, C-IV, D-III
• D. A-IV, B-III, C-II, D-I

Hint:

To determine the number of unpaired electrons in coordination complexes, consider the oxidation state of the central metal atom, its electronic configuration, and whether the ligand is a strong or weak field ligand

Answer 1

The Correct Option is A

Analysis of Complexes and Unpaired Electrons: 

1. Option (A) : The complex [Cr(CN)₆]³⁻ contains Cr³⁺ with an electronic configuration of 3d³. Cyanide (CN⁻) is a strong field ligand (SFL), which causes pairing of electrons.
   Number of unpaired electrons = 3.
2. Option (B) : The complex [Fe(H₂O)₆]²⁺ contains Fe²⁺ with an electronic configuration of 3d⁶. Water (H₂O) is a weak field ligand (WFL), which does not cause electron pairing.
   Number of unpaired electrons = 4.
3. Option (C) : The complex [Co(NH₃)₆]³⁺ contains Co³⁺ with an electronic configuration of 3d⁶. Ammonia (NH₃) is a strong field ligand (SFL), which causes pairing of electrons.
   Number of unpaired electrons = 0.
4. Option (D) : The complex [Ni(NH₃)₆]²⁺ contains Ni²⁺ with an electronic configuration of 3d⁸. Ammonia (NH₃) is a strong field ligand (SFL), which causes partial pairing of electrons.
   Number of unpaired electrons = 2.

Final Matching: A-II, B-IV, C-I, D-III

The correct answer is option (1).