Question

Identify the increasing order of effective magnetic moment of following elements in their +2 oxidation state.
(Fe $(Z=26)$, Co $(Z=27)$, Ni $(Z=28)$, Cu $(Z=29)$)

• A. Fe < Co < Ni < Cu
• B. Cu < Ni < Co < Fe
• C. Cu < Co < Fe < Ni
• D. Co < Cu < Fe < Ni

Hint:

More unpaired electrons mean higher magnetic moment.

Answer 1

The Correct Option is B

Step 1: Recall the relation of magnetic moment.
Effective magnetic moment depends on the number of unpaired electrons and is given by:
\[ \mu = \sqrt{n(n+2)}\ \text{BM} \]
where $n$ is the number of unpaired electrons.
Step 2: Determine electronic configurations in +2 state.
Fe$^{2+}$ : $3d^6$ → 4 unpaired electrons
Co$^{2+}$ : $3d^7$ → 3 unpaired electrons
Ni$^{2+}$ : $3d^8$ → 2 unpaired electrons
Cu$^{2+}$ : $3d^9$ → 1 unpaired electron
Step 3: Compare magnetic moments.
As the number of unpaired electrons increases, the magnetic moment increases.
Step 4: Arrange in increasing order.
\[ \text{Cu}<\text{Ni}<\text{Co}<\text{Fe} \]
Step 5: Conclusion.
The correct increasing order of effective magnetic moment is Cu < Ni < Co < Fe.