Which of the following elements has the largest atomic radius?

• A. Al
• B. Mg
• C. K
• D. Na

Answer: (C)

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 elements in the periodic table: Mg (magnesium) and Al (aluminum) are in period 3, with Al to the right of Mg; Na (sodium) and K (potassium) are in groups 1, with Na in period 3 and K in period 4.
4. Compare the elements by their group and period: K is below Na in group 1, so K has more electron shells than Na, Mg, and Al, which means K has the largest atomic radius.
5. Conclude that among the given elements, potassium (K) has the largest atomic radius because it is located further down the periodic table in the same group, resulting in a larger size.