Which one of the following atoms has the largest atomic radius?

• A. Al
• B. Si
• C. Na
• D. Mg

Answer: (C)

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 (Na, Mg, Al, Si) in the periodic table: all are in the same period (Period 3), with Na on the far left and Si towards the right.
3. Understand that since all these elements are in the same period, the element furthest to the left (Na) will have the largest atomic radius because it has the least effective nuclear charge attracting its electrons.
4. Recognize that as you move from Na to Si, the number of protons increases, pulling the electron cloud closer and decreasing the atomic radius.
5. Conclude that among Na, Mg, Al, and Si, sodium (Na) has the largest atomic radius because it is the leftmost element in the period.