Which of the following atoms has the largest atomic radius?

• A. Mg
• B. Al
• C. Si
• 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 due to increasing nuclear charge pulling electrons closer to the nucleus.
2. Identify the positions of the given elements (Mg, Al, Si, and Na) on the periodic table: Na is in period 3, group 1; Mg is period 3, group 2; Al is period 3, group 13; Si is period 3, group 14.
3. Since all these elements are in the same period (period 3), compare their group numbers: Na (group 1) has the fewest protons, so it has the least effective nuclear charge pulling on its electrons.
4. Understand that with fewer protons and the same energy level, Na's outer electrons experience less attraction to the nucleus, resulting in a larger atomic radius compared to Mg, Al, and Si.
5. Conclude that among the listed atoms, Na has the largest atomic radius because it is furthest to the left in the same period, meaning its electrons are held less tightly and spread out more.