Question

Which of the following cations has the maximum number of unpaired electrons?

• A. \(\text{Ni}^{2+}\)
• B. \(\text{Zn}^{2+}\)
• C. \(\text{Fe}^{3+}\)
• D. \(\text{Sc}^{2+}\)

Hint:

Write the d-electron count of each ion and count the unpaired electrons.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept
Count \(d\) electrons of each cation, then the unpaired electrons using Hund's rule.

Step 2: Ni2+ and Zn2+
\(\text{Ni}^{2+}\): \(3d^{8}\) with 2 unpaired electrons.
\(\text{Zn}^{2+}\): \(3d^{10}\) with 0 unpaired electrons.

Step 3: Fe3+ and Sc2+
\(\text{Fe}^{3+}\): \(3d^{5}\) with 5 unpaired electrons.
\(\text{Sc}^{2+}\): \(3d^{1}\) with 1 unpaired electron.

Step 4: Compare
The maximum is 5, for \(\text{Fe}^{3+}\).

Final Answer:
Fe3+ has the maximum number of unpaired electrons, which is 5. \[ \boxed{\text{(C) }\text{Fe}^{3+}} \]