Concept:The size of an ion changes when electrons are lost or gained by the parent atom.
Explanation:When a neutral atom loses electrons, it forms a positively charged ion called a cation.
The number of protons in the nucleus remains the same, but the number of electrons decreases.
With fewer electrons, the attractive pull of the nucleus is stronger on the remaining electrons.
Also, electron-electron repulsion is reduced.
These effects make the cation smaller than the parent atom.
On the other hand, anions gain electrons, so their size becomes larger than the parent atom.
Atomic size actually increases down a group and decreases across a period.
Therefore, the correct statement is that cations are smaller than the parent atom.
Answer:D. Cations are smaller than the parent atom.