So we synthesize Fadh two inside protein complex number one and then we oxidize it back into Fad plus in the process releasing those electrons. As the electrons travel through protein complex three and four we once again pump our H plus ions in this case only two, in this case, four. And as we pump them, we create our electrochemical gradient that is used by ATP synthase to synthesize our ATP molecules. Now, unlike NADH, our fadh two only Synthesizes two ATP per a single fadh two. And the reason for that is because our Fadh two begins on protein complex two but the NADH begins on protein complex number one to the left. And NADH basically pumps four more protons than Fadh two because NADH begins earlier, before Fadh two.