Which of the following lists the elements Mg, Na, P, Si, and Ar in order of increasing atomic radius?

• A. Na < Mg < Si < P < Ar
• B. Ar < Si < P < Na < Mg
• C. Mg < Na < Si < P < Ar
• D. Ar < P < Si < Mg < Na

Answer: (D)

Verified step by step guidance

1. Recall that atomic radius generally increases as you move down a group (column) in the periodic table and decreases as you move from left to right across a period (row).
2. Identify the positions of the elements Mg, Na, P, Si, and Ar on the periodic table: Na and Mg are in period 3, group 1 and 2 respectively; Si and P are in period 3, groups 14 and 15; Ar is a noble gas in period 3, group 18.
3. Since all elements are in the same period (period 3), compare their atomic radii by considering their group number: atomic radius decreases from left to right across the period due to increasing effective nuclear charge pulling electrons closer.
4. Order the elements from smallest to largest atomic radius by starting with the element farthest to the right (Ar) and moving leftward: Ar < P < Si < Mg < Na.
5. Confirm that this order matches the trend of increasing atomic radius across period 3, where noble gases have the smallest radius and alkali metals have the largest.