Chapter 2 - Atoms, Molecules, and Ions - Questions & Problems - Page 71: 2.77

Please see the answer below.

Anions are formed by the addition of electrons to their parent atom. So the number of electrons in an anion is always greater than the number of protons. As a result, the effective nuclear charge per electron in an anion is less than that of the parent atom. The less nuclear attraction causes an increase in the size of the anion. Cations are formed by the removal of electrons from their parent atom. So the number of protons in a cation is always greater than the number of electrons. As a result, the effective nuclear charge per electron in a cation is greater than that of the parent atom. The strong nuclear attraction causes a decrease in the size of the cation.