Which of the following elements has the largest atomic radius?

• A. Al
• 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. Also remember that atomic radius generally decreases as you move from left to right across a period (row) due to increasing nuclear charge pulling electrons closer to the nucleus.
3. Identify the positions of the given elements (Al, Mg, Na, and K) on the periodic table: Na, Mg, and Al are all in period 3, while K is in period 4, one row below them.
4. Since K is below Na, Mg, and Al in the periodic table, it has an additional electron shell, which increases its atomic radius compared to the others.
5. Therefore, by comparing their positions and applying periodic trends, K has the largest atomic radius among the listed elements.