Chemistry - Atomic Structure Question with Solution | TestHub

To determine the quantum numbers for the last electron of K⁺, first find the electron configuration of K (Potassium), which is [Ar] $4s^1$. K⁺ is formed by losing the $4s^1$ electron, making its configuration [Ar]. The last electron of K⁺ is therefore the last electron of Argon, which is $3p^6$. For $3p^6$, the quantum numbers are $n=3$, $l=1$, $m_l=-1$, $m_s=-1/2$.

The quantum numbers are:

$n=3$ (principal quantum number for the 3rd shell)

$l=1$ (azimuthal quantum number for a p-orbital)

$m_l=-1$ (magnetic quantum number for the last electron in the $3p$ subshell, filling $3p_x$, $3p_y$, $3p_z$ with two electrons each, the last electron would be in $3p_x$ with $m_l=-1$)

$m_s=-1/2$ (spin quantum number, as it's the second electron in that orbital, it has a down spin)

Therefore, the correct option is B: $3,1,-1,-1/2$.