Which of the following atoms has the largest atomic radius?

• A. Mg
• B. Na
• C. Li
• D. K

Answer: (B)

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 group and period for each element: Li (Group 1, Period 2), Na (Group 1, Period 3), K (Group 1, Period 4), and Mg (Group 2, Period 3).
4. Since Li, Na, and K are all in Group 1, their atomic radius increases down the group, so K should have a larger radius than Na, and Na larger than Li. Mg is in Group 2 and Period 3, so it generally has a smaller radius than Na in the same period.
5. Compare the positions: K is the lowest in Group 1, so it has the largest atomic radius, followed by Na, then Li, and Mg is smaller than Na because it is in Group 2. Therefore, K should have the largest atomic radius among the options.