Which of the following elements has the smallest atomic radius?

• A. Na
• B. Cl
• C. Ne
• D. Mg

Answer: (C)

Verified step by step guidance

1. Understand 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 elements Na, Mg, Cl, and Ne in the periodic table: all are in the same period (Period 3), with Na and Mg on the left side, Cl towards the right, and Ne at the far right end.
3. Recall that noble gases like Ne have a full outer electron shell, resulting in a strong effective nuclear charge and thus a smaller atomic radius compared to other elements in the same period.
4. Compare the elements by their position: since Ne is furthest to the right in Period 3, it experiences the greatest effective nuclear charge and therefore has the smallest atomic radius.
5. Conclude that among Na, Mg, Cl, and Ne, neon (Ne) has the smallest atomic radius due to its position and electron configuration.