Consider the ionic and neutral species , , , and . Which of these species possess exactly the same n — Periodic Table and Periodicity Chemistry Question

💡 Solution & Explanation

$Cr$ ($Z=24$) is $3d^5 4s^1$ (5 d-electrons). $Mn$ ($Z=25$) is $3d^5 4s^2$, so $Mn^{2+}$ is $3d^5$ (5 d-electrons). $Fe$ ($Z=26$) is $3d^6 4s^2$, so $Fe^{3+}$ is $3d^5$ (5 d-electrons). $Co$ ($Z=27$) is $3d^7 4s^2$, so $Co^{3+}$ is $3d^6$ (6 d-electrons). Thus, $Cr$, $Mn^{2+}$, and $Fe^{3+}$ all have 5 d-electrons.