Question

The number of unpaired electrons in \( Cu^{2+} \) is

• A. 2
• B. 3
• C. 1
• D. 4

Hint:

\( Cu^{2+} \) is \( 3d^{9} \); count the unpaired electrons in a \( d^{9} \) set.

Answer 1

The Correct Option is C

Step 1: Copper has atomic number 29, so its ground-state configuration is \( [Ar]3d^{10}4s^{1} \).
Step 2: To form \( Cu^{2+} \), two electrons are removed. The 4s electron leaves first, then one 3d electron, giving \( Cu^{2+} = [Ar]3d^{9} \).
Step 3: In \( 3d^{9} \) the five d-orbitals hold 9 electrons: four orbitals are fully paired (8 electrons) and one orbital has a single electron.
Step 4: Hence there is exactly 1 unpaired electron.
Answer: 1.