Answer:
Calcium is larger than magnesium, and has a smaller ionization energy. This means that calcium is less likely to gain electrons when compared to magnesium.
Step-by-step explanation:
Calcium is larger than magnesium because it has a higher atomic weight, 40.078 to 20.305
Calcium has a smaller ionization energy because it has more energy levels of electrons, meaning that the electrons will be farther away from the nucleus so will have less attraction to it.
Calcium is less likely to gain electrons because its ionization energy is lower than magnesium. A high value of ionization energy shows a high attraction between the electron and the nucleus. Since calcium's ionization energy is lower, it will have less attraction between the electron and nucleus.