Excitation of an electron is an elevation in energy level of the valence electron above the ground state electron.
When an electron gains energy, usually the outermost electron it moves from a orbital of lower energy to a orbital of higher energy, the element is in an excited state.
The electron configuration of ground state of magnesium is 1s2 2s2 2p6 3s1 3p2, when it gains energy the electronic configuration is 1s2 2s2 2p6 3s1 3p1 the excited state of Magnesium this is because the last electron moves from the 3S orbital to a higher energy orbital 3P
