Which of the following elements has the largest atomic radius?

• A. Li
• B. Mg
• C. Na
• D. K

Answer: (D)

Verified step by step guidance

1. Recall that atomic radius generally increases as you move down a group (column) in the periodic table because additional electron shells are added, making the atom larger.
2. Recall that atomic radius generally decreases as you move from left to right across a period (row) in the periodic table due to increasing nuclear charge pulling electrons closer to the nucleus.
3. Identify the positions of the given elements (Li, Mg, Na, and K) on the periodic table: Li and Na are in Group 1 (alkali metals), Mg is in Group 2 (alkaline earth metals), and K is also in Group 1 but in the period below Na.
4. Compare the elements by group and period: K is below Na and Li in Group 1, so it has more electron shells, which increases its atomic radius compared to Li, Na, and Mg.
5. Conclude that K has the largest atomic radius among the given elements because it is further down the group, outweighing the effect of increasing nuclear charge.