Final answer:
Oxygen (O2) cannot serve as the terminal electron acceptor in anaerobic respiration; it is the exclusive acceptor in aerobic respiration. Sulfur, iron, and protons can all be used as electron acceptors in anaerobic respiration.
Step-by-step explanation:
The subject in question is anaerobic respiration. The terminal electron acceptor in anaerobic respiration can be an inorganic molecule other than oxygen, such as sulfate or nitrate. However, oxygen (O2) is the terminal electron acceptor exclusively in aerobic respiration. Therefore, all the mentioned molecules except O2 can serve as terminal electron acceptors in anaerobic respiration. During anaerobic conditions, alternative electron transport system carriers are used by microbes, with some having an intact Krebs cycle. On the other hand, aerobic respiration requires oxygen to produce ATP efficiently, utilizing the energy from high-energy electrons carried by NADH or FADH₂.