Question

Which cation from following develops least magnetic moment?

• A. \(\mathrm{Cu}^{2+}\)
• B. \(\mathrm{Cr}^{3+}\)
• C. \(\mathrm{Co}^{2+}\)
• D. \(\mathrm{Fe}^{2+}\)

Hint:

Magnetic moment depends on unpaired electrons: \(\mu = \sqrt{n(n+2)}\). Fewer unpaired electrons means lower moment.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept
Spin-only magnetic moment is \(\mu = \sqrt{n(n+2)}\) BM, where \(n\) is the number of unpaired electrons.

Step 2: Electronic configurations
\(\text{Cu}^{2+}: 3d^{9}\) gives 1 unpaired electron.
\(\text{Cr}^{3+}: 3d^{3}\) gives 3.
\(\text{Co}^{2+}: 3d^{7}\) gives 3.
\(\text{Fe}^{2+}: 3d^{6}\) gives 4.

Step 3: Compare the options
\(\text{Cu}^{2+}\) has the fewest unpaired electrons, so it has the least magnetic moment, about 1.73 BM.

Final Answer:
\(\text{Cu}^{2+}\) has the least magnetic moment. \[ \boxed{\text{(A) }\text{Cu}^{2+}} \]