Which of the following atoms has the smallest atomic radius?

• A. K
• B. F
• C. Li
• D. Na

Answer: (B)

Verified step by step guidance

1. Understand that atomic radius generally decreases across a period (left to right) on the periodic table and increases down a group (top to bottom).
2. Identify the positions of the given elements: K (potassium), Li (lithium), Na (sodium), and F (fluorine) on the periodic table. K, Li, and Na are alkali metals in Group 1, while F is a halogen in Group 17.
3. Note that K, Na, and Li are all in Group 1 but in different periods: Li is in period 2, Na in period 3, and K in period 4. Atomic radius increases down a group, so K > Na > Li in size.
4. Fluorine (F) is in period 2, group 17, which means it is to the right of lithium (Li) in the same period. Since atomic radius decreases across a period, F has a smaller radius than Li.
5. Conclude that among the given atoms, fluorine (F) has the smallest atomic radius because it is further to the right in the same period compared to Li, and all alkali metals listed are larger due to their position in Group 1 and/or lower periods.