The atomic number of Chromium (Cr) is 24. Which of the following sets of quantum numbers could corre — Atomic Structure Chemistry Question

💡 Solution & Explanation

According to the Aufbau principle, after Argon ($18$), the $4s$ subshell fills ($19^{\text{th}}, 20^{\text{th}}$), followed by the $3d$ subshell. The $21^{\text{st}}$ to $24^{\text{th}}$ electrons enter $3d$. For a $3d$ electron, $n=3$ and $l=2$. The magnetic quantum number $m$ can be any integer from $-2$ to $+2$. Option B is the only one matching $n=3, l=2$. Note: While Cr anomalously assumes $4s^1 3d^5$, the last set of electrons to enter energetically are still $3d$.