Question

Which of the following has highest spin only magnetic moment

• A. $Cr^{2+}$
• B. $Mn^{2+}$
• C. $Fe^{2+}$
• D. $Ni^{2+}$

Hint:

Shortcut Tip: Maximum magnetic moment occurs for maximum unpaired electrons. \(d^5\) configuration has the highest spin-only magnetic moment among these ions.

Answer 1

The Correct Option is B

Concept:
Spin only magnetic moment depends on number of unpaired electrons. \[ \mu=\sqrt{n(n+2)}~BM \] where \(n\) is number of unpaired electrons.
Step 1:
\[ Cr^{2+}=[Ar]3d^4 \] \[ Mn^{2+}=[Ar]3d^5 \] \[ Fe^{2+}=[Ar]3d^6 \] \[ Ni^{2+}=[Ar]3d^8 \]
Step 2:
\[ Cr^{2+}\rightarrow 4 \] \[ Mn^{2+}\rightarrow 5 \] \[ Fe^{2+}\rightarrow 4 \] \[ Ni^{2+}\rightarrow 2 \]
Step 3:
More unpaired electrons means larger magnetic moment. \[ Mn^{2+} \] has maximum unpaired electrons.
Step 4:
Hence highest spin only magnetic moment is: \[ \boxed{Mn^{2+}} \] \[ \boxed{\text{Correct Option = (2)}} \]