Which of the following atoms has the smallest atomic radius?

• A. Li
• B. O
• C. Na
• D. F

Answer: (D)

Verified step by step guidance

1. Understand that atomic radius generally decreases across a period (left to right) in the periodic table due to increasing nuclear charge pulling electrons closer, and increases down a group due to the addition of electron shells.
2. Identify the positions of the given atoms in the periodic table: Li (Lithium) and Na (Sodium) are in Group 1, with Na below Li; O (Oxygen) and F (Fluorine) are in Period 2, Group 16 and Group 17 respectively.
3. Compare the atomic radii of Li and Na: since Na is below Li in Group 1, Na has a larger atomic radius than Li due to an extra electron shell.
4. Compare O and F, which are in the same period: F has a higher nuclear charge than O, so F's electrons are pulled closer, resulting in a smaller atomic radius.
5. Finally, compare the smallest radii from each group: F (Period 2, Group 17) will have a smaller atomic radius than Li and Na (Group 1), and also smaller than O, because it is further right in the same period, confirming F has the smallest atomic radius.