Which of the following statements correctly describes the periodic trend in atomic radius?

• A. Atomic radius decreases down a group and increases across a period from left to right.
• B. Atomic radius increases down a group and decreases across a period from left to right.
• C. Atomic radius remains constant both down a group and across a period.
• D. Atomic radius increases both down a group and across a period from left to right.

Answer: (B)

Verified step by step guidance

1. Understand that atomic radius refers to the size of an atom, typically measured from the nucleus to the outer boundary of the electron cloud.
2. Recall the periodic trends: as you move down a group (column) in the periodic table, new electron shells are added, which increases the atomic radius because electrons are farther from the nucleus.
3. Recognize that as you move across a period (row) from left to right, the number of protons in the nucleus increases, which pulls the electron cloud closer due to greater effective nuclear charge, thus decreasing the atomic radius.
4. Combine these observations to conclude that atomic radius increases down a group and decreases across a period from left to right.
5. Use this understanding to evaluate the given statements and identify the one that correctly describes the periodic trend in atomic radius.