The number of core electrons present in Magnesium is

The electronic configuration of Mg is as follows.

${}_{12}\mathrm{Mg}\to 1{\mathrm{s}}^{2}2{\mathrm{s}}^{2}2{\mathrm{p}}^{6}3{\mathrm{s}}^2$

In this configuration valence shell is M shell or 3rd shell

The number of valence electrons is 2

Core electrons : The number of electrons other than valence electrons in the electronic configuration of an element is known as core electrons.

The number of core electrons in the Mg configuration is 10.