Answer: The correct answer is Electron transport chain.
Electron transport chain is a series of protein and organic molecules present in the inner membrane of mitochondria that help in the transfer of electrons from higher energy to lower energy state. Reduced electron carriers that is FADH₂ and NADH transfer electrons via the these organic complexes through redox reactions and finally electrons are accepted by oxygen. The redox reactions capture energy in the form of proton gradient.
The proton gradient helps in the generation of large amount of ATP molecules through chemiosmosis.
Therefore, electron transport chain is an integral part of aerobic respiration.