Question

Match List - I with List - II.

List - I		List - II
(a)	[Fe(CN)6]3−	(i)	5.92 BM
(b)	[Fe(H2O)6]3+	(ii)	0 BM
(c)	[Fe(CN)6]4−	(iii)	4.90 BM
(d)	[Fe(H2O)6]2+	(iv)	1.73 BM

Choose the correct answer from the options given below.

• A. (a)-(iv), (b)-(i), (c)-(ii), (d)-(iii)
• B. (a)-(iv), (b)-(ii), (c)-(i), (d)-(iii)
• C. (a)-(ii), (b)-(iv), (c)-(iii), (d)-(i)
• D. (a)-(i), (b)-(iii), (c)-(iv), (d)-(ii)

Answer 1

The Correct Option is A

To solve this problem, we need to match each complex ion in List I with its correct magnetic moment in List II by calculating the spin-only magnetic moment for each complex. The magnetic moment is given in Bohr Magneton (BM), and it depends on the number of unpaired electrons. The formula for calculating the magnetic moment (\( \mu \)) is: 

\(\mu = \sqrt{n(n+2)} \, \text{BM}\)

Here, \( n \) is the number of unpaired electrons in the complex.

1. [Fe(CN)₆]³⁻: In this complex, the Fe is in the +3 oxidation state (Fe³⁺), which implies the electronic configuration of Fe³⁺ is 3d⁵. In the presence of the strong field ligand CN^-, all electrons get paired, resulting in zero unpaired electrons. Therefore, the magnetic moment is 0 BM.
2. [Fe(H₂O)₆]³⁺: Here, Fe is also in the +3 oxidation state (Fe³⁺), with the electronic configuration 3d⁵. Water (H₂O) is a weak field ligand, so electrons are not paired up significantly, resulting in 5 unpaired electrons. The magnetic moment is calculated as follows: \(\mu = \sqrt{5(5+2)} = \sqrt{35} \approx 5.92 \, \text{BM}\)
3. [Fe(CN)₆]⁴⁻: In this complex, Fe is in the +2 oxidation state (Fe²⁺), which implies the electronic configuration of Fe²⁺ is 3d⁶. With CN^- being a strong field ligand, and forming a low spin complex, all electrons are paired, resulting in zero unpaired electrons. Therefore, the magnetic moment is 0 BM.
4. [Fe(H₂O)₆]²⁺: Here, Fe is in the +2 oxidation state (Fe²⁺), with the electronic configuration 3d⁶. Water (H₂O) is a weak field ligand resulting in 4 unpaired electrons because it is a high spin complex. The magnetic moment is: \(\mu = \sqrt{4(4+2)} = \sqrt{24} \approx 4.90 \, \text{BM}\)

Based on these calculations and reasoning, the correct matching is:

• (a) - (ii)
• (b) - (i)
• (c) - (ii)
• (d) - (iii)

Thus, the option (a)-(iv), (b)-(i), (c)-(ii), (d)-(iii) is the correct answer.