Final answer:
Magnesium and calcium have similar ionization energies because they are in the same group and have the same number of valence electrons.
Step-by-step explanation:
Magnesium and calcium have similar ionization energies. The ionization energy is the energy required to remove an electron from an atom. In general, ionization energy tends to increase as you move across a periodic table period from left to right. However, for magnesium and calcium, both elements are in the same group (Group 2) and have the same number of valence electrons, so their ionization energies are similar.