Final answer:
Argon does not belong in the list with Calcium, Sodium, and Iron as it is a noble gas, whereas the others are metals.
Step-by-step explanation:
The element that does not belong in the list which includes Calcium, Sodium, Iron, and Argon is Argon. The reason is that Calcium, Sodium, and Iron are all metals, whereas Argon is a noble gas and considered a nonmetal. While Calcium is an alkaline earth metal (Group 2), Sodium is an alkali metal (Group 1), and Iron is a transition metal, Argon is placed in a completely different category in the periodic table (Group 18), known for its lack of reactivity due to a full set of valence electrons.