Step-by-step explanation:
The electronic configuration of an atom can be represented by either sublevel notation or using shell notations.
Sublevel notations shows the sequence of filling electrons into the orbitals of the sublevels.
Shell notations are used to denote the electrons in all orbitals of each energy level.
Element Number of electrons Sub-level notation shell notation
Mg 12 1s² 2s² 2p⁶ 3s² 2 8 2