Which of the following atoms has the largest atomic radius?

• A. Si
• B. Al
• C. Mg
• D. Na

Answer: (D)

Verified step by step guidance

1. Recall that atomic radius generally decreases from left to right across a period in the periodic table due to increasing nuclear charge pulling electrons closer to the nucleus.
2. Recall that atomic radius generally increases down a group because additional electron shells are added, increasing the size of the electron cloud.
3. Identify the positions of the given elements (Si, Al, Mg) and the correct answer (Na) on the periodic table: all are in period 3, but Na is to the far left, Mg next, then Al, and Si further right.
4. Understand that since Na is the furthest to the left in period 3, it has the smallest effective nuclear charge experienced by its outer electrons, resulting in the largest atomic radius among these elements.
5. Therefore, compare the elements by their position in the periodic table and conclude that Na has the largest atomic radius because it has the fewest protons in period 3, leading to less pull on its electrons and a larger size.