Which statement best explains why calcium has a larger atomic radius than magnesium? a. calcium has a stronger nuclear charge than magnesium. b. calcium has electrons in more energy levels than magnesium. c. calcium has more neutrons than magnesium. d. calcium’s third energy level contains more electrons than magnesium’s.

Electron shielding effects reduces the effect of a full nuclear charge. As more of the core electrons are added, they begin to 'shield' the valence electrons from the increasingly positive nucleus. But this will allow the outer electrons to move farther away from the nucleus, hence increasing atomic size. The electron shielding effect is responsible for the increase in atomic size moving down groups.

B. Calcium has electrons in more energy levels than magnesium.

B. Calcium has electrons in more energy levels than magnesium.