Final answer:
Sulfur (D) is the atom from the options provided that would exhibit an expanded octet as it is an element from the third period of the periodic table which can have more than eight electrons in its valence shell.
Step-by-step explanation:
The atom that would exhibit an expanded octet among the options provided is D. Sulfur. Elements in the second period of the periodic table (like Carbon, Nitrogen, and Oxygen) can only accommodate eight electrons in their valence shells due to having only four valence orbitals. In contrast, elements in the third period or beyond, such as Sulfur, have access to d orbitals starting in the third period, allowing them to have more than eight electrons around the central atom. Molecules formed from these elements, like phosphorus pentachloride (PCl5), can have expanded octets, also known as hypervalent molecules.