Final answer:
The element that typically has the largest atomic radius and is the least dense in its period is Sodium (Na).
Step-by-step explanation:
The element that typically has the largest atomic radius and is the least dense in its period is Sodium (C).
The atomic radius is a measure of the atomic size, and it generally increases down each group and decreases along each period of the periodic table. Therefore, in the same period, the element with the largest atomic radius will be found in the lower left corner of the periodic table.
Sodium (Na) is found in group 1 and period 3, and it has a larger atomic radius compared to the other options (Lithium, Oxygen, and Chlorine). It is also less dense than the other elements in its period.