Final answer:
Among the substances listed, solid iron (Fe) has the lowest entropy due to its simple atomic structure and lack of complex molecular motion compared to molecules in a gaseous or liquid state.
Step-by-step explanation:
For which of the following substances would entropy (S) be the lowest? The substances listed are NH₃(g), H₂O(s), Fe(s), N₂(g), H₂O(l). Entropy is a measure of the disorder or randomness in a system. A substance in the gaseous state will have higher entropy than the same substance in a liquid or solid state due to the greater freedom of movement of the molecules. Among solids, a pure element like iron (Fe) will have lower entropy compared to a molecular solid such as water ice (H₂O(s)) because there is less complexity in the arrangement of iron atoms. Therefore, Fe(s) has the lowest entropy among the listed substances.
Solid iron (Fe) lacks the complexity and freedom of motion present in molecular structures and phases such as gases and liquids, therefore we can conclude that Fe(s) has the lowest entropy. The correct answer is C) 3 only.