Past exam of the chemistry course of the year 1 of the natural sciences course of the University of Cambridge / 2023 / Paper 1 / 6 / b / i / Solution

The valence configurations are $\mathrm{C}:2s^{2}2p^2$, $\mathrm{Si}:3s^{2}3p^2$, and $\mathrm{Pb}:6s^{2}6p^2$. Their full closed-shell cores are respectively $[\mathrm{He}]$, $[\mathrm{Ne}]$, and $[\mathrm{Xe}]4f^{14}5d^{10}$. The filled 4f and 5d subshells of lead are not the outer valence configuration requested.