Final answer:
The last site of electrons in the electron transport chain before being transferred to oxygen is the cytochrome oxidase complex, or Complex IV, which is responsible for the reduction of oxygen to water.
Step-by-step explanation:
Prior to being transferred to oxygen, the last site of electrons in the electron transport chain is the cytochrome oxidase complex, also known as Complex IV. Complex IV is the final complex in the sequence of the electron transport chain and is responsible for reducing oxygen into water. This complex contains several subunits, two heme groups, and metal ion cofactors, including copper, magnesium, and zinc. The electrons pass from cytochrome c to Complex IV where, with protons and oxygen, water is formed. This is the terminal stage of the electron transport chain, which is a crucial part of cellular respiration and aerobic respiration, taking place in the inner mitochondrial membrane of eukaryotes and the plasma membrane of prokaryotes.