Final answer:
Cations are smaller than their parent atoms because they lose electrons, which leads to a reduced electron cloud and increased effective nuclear charge, resulting in a smaller atomic radius.
Step-by-step explanation:
The reason cations are smaller than their parent atoms is because cations lose electrons. When an atom loses one or more electrons to form a cation, two significant changes occur: the electron cloud shrinks since there is now one fewer occupied principal energy level, and the remaining electrons are more strongly attracted to the nucleus. This stronger attraction is due to an increase in the effective nuclear charge; there are more protons than electrons left in the atom, leading to a net positive charge. This results in a smaller atomic radius for the cation compared to the parent atom.
Another contributing factor to the reduced size of cations compared to their parent atoms is the decreased electron-electron repulsion. With fewer electrons, the repulsion between them is less, allowing the electrons to be pulled closer to the nucleus.
Therefore, the correct answer is b) Cations lose electrons. This loss of electrons causes a reduction in the atomic radius, making the cation smaller than its parent atom.