To determine the electron configuration for the \( \text{Co}^{2+} \) ion, we need to start from the electron configuration of the neutral cobalt (Co) atom and then account for the loss of electrons during ionization.
1. Determine the electron configuration of the neutral Co atom:
Cobalt (Co) has an atomic number of 27, which means a neutral cobalt atom has 27 electrons. The electron configuration for cobalt is:
[tex]\[
\text{Co}: [\text{Ar}] \, 4s^2 \, 3d^7
\][/tex]
2. Form the \( \text{Co}^{2+} \) ion:
To form the \( \text{Co}^{2+} \) ion, cobalt loses 2 electrons. Electrons are removed first from the outermost shell, which is the \( 4s \) orbital, followed by the \( 3d \) orbital if necessary. In this case, the two electrons are removed from the \( 4s \) orbital:
[tex]\[
\text{Co}^{2+}: [\text{Ar}] \, 3d^7
\][/tex]
Thus, the electron configuration for the \( \text{Co}^{2+} \) ion is:
[tex]\[
[\text{Ar}] \, 3d^7
\][/tex]
Therefore, the correct answer is:
[tex]\[
[\operatorname{Ar}] \, 3d^7
\][/tex]
