Which of the following elements has the largest atomic radius?

• A. Na
• B. Mg
• C. Al
• 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 because the increasing nuclear charge pulls the electrons closer to the nucleus.
3. Identify the positions of the elements Na, Mg, Al, and K on the periodic table: Na, Mg, and Al are all in period 3, while K is in period 4, one row below Na.
4. Since K is below Na in the same group (alkali metals for Na and K), K has an additional electron shell compared to Na, making its atomic radius larger than Na, Mg, and Al.
5. Therefore, by comparing their positions and applying periodic trends, K has the largest atomic radius among the given elements.