Which of the following elements has the largest atomic radius?

• A. K
• B. Al
• C. Mg
• D. Na

Answer: (A)

Verified step by step guidance

1. Understand that atomic radius generally increases as you move down a group in the periodic table because additional electron shells are added, making the atom larger.
2. Recognize that atomic radius generally decreases as you move from left to right across a period due to increasing nuclear charge pulling electrons closer to the nucleus.
3. Identify the positions of the elements in the periodic table: K (potassium) and Na (sodium) are in Group 1, while Mg (magnesium) and Al (aluminum) are in Groups 2 and 13 respectively, all in the same period except K which is in the period below.
4. Compare the elements by their group and period: since K is below Na in Group 1, it has an additional electron shell, making its atomic radius larger than Na, Mg, and Al.
5. Conclude that among the given elements, potassium (K) has the largest atomic radius due to its position in the periodic table.