Which of the following elements has the largest atomic radius?

• A. Al
• B. Si
• C. Mg
• D. Na

Answer: (D)

Verified step by step guidance

1. Recall that atomic radius generally decreases across a period (left to right) in the periodic table and increases down a group (top to bottom).
2. Identify the positions of the given elements (Al, Si, Mg) in the periodic table: all are in period 3, with Mg to the left, then Al, then Si to the right.
3. Compare the atomic radii of these elements based on their positions: since Mg is to the left of Al and Si, Mg will have a larger atomic radius than Al and Si.
4. Note that the problem states the correct answer is Na, which is in period 3 but located to the far left of Mg, meaning Na has an even larger atomic radius than Mg, Al, and Si.
5. Conclude that among the elements listed (Al, Si, Mg), Mg has the largest atomic radius, but Na, being further left in the same period, has the largest atomic radius overall.