Question

How many unpaired electrons are present in the element of atomic number 27 with a +2 oxidation state?

• A. \(1\)
• B. \(2\)
• C. \(3\)
• D. \(0\)

Hint:

For transition metals, the number of unpaired electrons can be found by looking at the electronic configuration of the ion.

Answer 1

The Correct Option is C

The element with atomic number 27 is cobalt (Co). The electronic configuration of neutral Co is: \[ \text{Co}: [Ar] 3d^7 4s^2. \] In the +2 oxidation state, cobalt loses two electrons, which come from the 4s orbital, giving: \[ \text{Co}^{2+}: [Ar] 3d^7. \] The 3d subshell can accommodate 10 electrons, and the configuration of \( 3d^7 \) means there are 3 unpaired electrons.