Given the elements Li, Na, and K, rank them in order of increasing atomic radius.

• A. Na < K < Li
• B. Na < Li < K
• C. K < Na < Li
• D. Li < Na < K

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 because each successive element has an additional electron shell, making the atom larger.
2. Identify the group to which Li, Na, and K belong. All three elements are in Group 1 (alkali metals), so their atomic radius trend will follow the group trend.
3. Compare the positions of Li, Na, and K in the periodic table: Li is in period 2, Na is in period 3, and K is in period 4, meaning K has the most electron shells, followed by Na, then Li.
4. Conclude that the atomic radius increases from Li to Na to K because the number of electron shells increases, which outweighs the effect of increasing nuclear charge in this group.
5. Therefore, the correct order of increasing atomic radius is: Li < Na < K.