Which of the following statements correctly describes the periodic trend of ionic radius?

• A. Ionic radius generally increases across a period from left to right.
• B. Ionic radius generally increases down a group.
• C. Anions are always smaller than their parent atoms.
• D. Cations are always larger than their parent atoms.

Answer: (B)

Verified step by step guidance

1. Understand that ionic radius refers to the size of an ion, which can be either a cation (positively charged) or an anion (negatively charged).
2. Recall the general periodic trends: as you move down a group in the periodic table, atoms gain more electron shells, which increases the size of the ion or atom.
3. Recognize that moving across a period from left to right, the number of protons increases, pulling electrons closer and generally decreasing atomic and ionic size, so ionic radius usually decreases across a period.
4. Know that anions (negatively charged ions) are larger than their parent atoms because they gain electrons, increasing electron-electron repulsion and expanding the electron cloud.
5. Know that cations (positively charged ions) are smaller than their parent atoms because they lose electrons, reducing electron-electron repulsion and allowing the remaining electrons to be pulled closer to the nucleus.