Which of the following elements has the largest atomic radius?

• A. Al
• B. Na
• C. K
• D. Mg

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 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: Na (Sodium) and K (Potassium) are in Group 1 (alkali metals), while Mg (Magnesium) and Al (Aluminum) are in Period 3 but in Groups 2 and 13 respectively.
4. Since K is below Na in Group 1, it has more electron shells, so its atomic radius is larger than Na's. Both Mg and Al are in Period 3, so their atomic radii are smaller than those of Na and K.
5. Therefore, by comparing group and period trends, K has the largest atomic radius among the given elements.