Which of the following elements has the smallest atomic radius?

• A. Al
• B. Na
• C. Mg
• D. Cl

Answer: (D)

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, and increases down a group due to added electron shells.
2. Identify the positions of the given elements in the periodic table: Na (Sodium) is in Group 1, Period 3; Mg (Magnesium) is in Group 2, Period 3; Al (Aluminum) is in Group 13, Period 3; Cl (Chlorine) is in Group 17, Period 3.
3. Since all elements are in the same period (Period 3), compare their atomic radii by considering their group number: atomic radius decreases as you move from left (Group 1) to right (Group 17) across the period.
4. Recognize that Cl, being furthest to the right among the listed elements, has the highest effective nuclear charge and thus the smallest atomic radius.
5. Conclude that Cl has the smallest atomic radius among the options because it is furthest to the right in the same period, resulting in a stronger pull on its electrons and a smaller size.