The correct option is D it is the final electron acceptor at the end of the electron transport chain
Cellular respiration, whether aerobic or anaerobic, is a metabolic process which converts nutrient energy into ATP and waste products.
Aerobic respiration uses the oxygen gathered during the process of anatomical respiration (or breathing) to facilitate ATP synthesis. In this role, oxygen is an electron acceptor within the electron transport chain which synthesizes ATP from nutrients.