Calcium is more reactive than Magnesium due to its lower ionization energy.
Work Step by Step
Magnesium, which has fewer orbitals than Calcium, has a smaller atomic radius than Calcium. As a result, Magnesium's nucleus exerts a stronger pull on its valence electrons than Calcium exerts on its valence electrons. Because it is easier to remove electrons from Calcium due to its lower ionization energy, Calcium is going to be more reactive than Magnesium.