Which of the following ions has five electrons in its outermost d subshell?

• A. Cr^{3+}
• B. Mn^{2+}
• C. Fe^{3+}
• D. Co^{2+}

Answer: (C)

Verified step by step guidance

1. Recall that the d subshell can hold a maximum of 10 electrons and that the number of d electrons in a transition metal ion depends on the element's atomic number and its charge.
2. Determine the electron configuration of the neutral atom for each element (Cr, Mn, Fe, Co) focusing on the d subshell electrons. For example, Fe (atomic number 26) has the electron configuration [Ar] 3d^6 4s^2.
3. Adjust the electron configuration for the ion by removing electrons according to the charge. Remember that electrons are removed first from the 4s subshell before the 3d subshell when forming cations.
4. Count the number of electrons remaining in the d subshell for each ion after accounting for the charge.
5. Identify which ion has exactly five electrons in its outermost d subshell based on the counts from the previous step.