About oxidative phosphorylation true is

In oxidative phosphorylation, ATP is produced by combining ADP and Pi with the energy generated by the flow of electrons from NADH to molecular oxygen in the electron transpo chain. There are three sites in the respiratory chain where ATP is formed by oxidative phosphorylation. These sites have been proved by the free energy changes of the various redox couples. Since hydrolysis of ATP to ADP + Pi releases around 7.3 K. Cal/mole, the formation ATP from ADP + Pi requires a minimum of around 8 KCal/mole. The formation of ATP is therefore not possible at the sites where the free energy released is less than 8 KCal/mole. Whenever two systems or redox couple of the respiratory chain differ from each other by 0.22 volts in standard redox potential (E'o), the free energy is sufficient to form ATP. Go = -n F Eo Go = -2 x 23.06 x 0.22 = -10.15 KCalRef: MN Chatterjea Textbook of Medical Biochemistry, 8th Edition, Page no: 143