Which metal will have the highest third ionization energy, magnesium or aluminum?
On the basis of its electronic structure, clearly magnesium metal will have the highest third ionization energy.
Consider the electronic configurations of aluminum, and magnesium.
Because the third ionization energy involves the removal of a
Now as a chemist, as a physical scientist, you should consult the data in order to establish that I am not telling pork pies. See here for a start.