Chemistry - GENERAL CHEMISTRY Question with Solution | TestHub

An $(18+2)$ electronic configuration refers to ions with a pseudo-noble gas core ($n{s}^{2}n{p}^{6}n{d}^{10}$) plus two electrons in the outermost s-orbital ($s^2$).

Ions that have an $(18+2)$ configuration:

$S{n}^{2+}$ ($[Kr]4d^{10}5s^2$) and $T{l}^{+}$ ($[Xe]4f^{14}5d^{10}6s^2$) fit this pattern.

Ions that do not have an $(18+2)$ configuration:

$Z{n}^{2+}$, $S{n}^{4+}$, and $T{l}^{3+}$ have a stable 18-electron (pseudo-noble gas) configuration.

$C{u}^{2+}$ ($3d^9$) and $F{e}^{2+}$ ($3d^6$) have incomplete d-subshells.

The total number of ions that do not have the $(18+2)$ configuration is 5.