The valence shell electronic configuration of magnesium is ________

1. Valence shell: It is the shell that is filled at the last while writing the electronic configuration.
2. The atomic number of magnesium ($\mathrm{Mg}$) is $12$.
3. Electronic configuration of $\mathrm{Mg}$ is $1{\mathrm{s}}^{2}2{\mathrm{s}}^{2}2{\mathrm{p}}^{6}3{\mathrm{s}}^2$.
4. Hence, the valence shell of $\mathrm{Mg}$ is ‘$3\mathrm{s}$’ and the number of electrons in the valence shell of magnesium is $2$.
5. Therefore, the valence shell electronic configuration of magnesium is $3{\mathrm{s}}^2$.