The chemiosmotic theory was given by
Chemiosmotic theory is postulated by the biochemist Peter Mitchell in 1961 to describe ATP synthesis by way of a proton electrochemical coupling. According to this theory, hydrogen ions (protons) are pumped from the mitochondrial matrix to the intermembrane space via the hydrogen carrier proteins while the electrons are transferred along the electron transport chain in the mitochondrial inner membrane. As the hydrogen ions accumulate in the intermembrane space, an energy-rich proton gradient is established. As the proton gradient becomes sufficiently intense the hydrogen ions tend to diffuse back to the matrix (where hydrogen ions are less) via the ATP synthase (a transport protein). As the hydrogen ions diffuse (through the ATP synthase) energy is released which is then used to drive the conversion of ADP to ATP (by phosphorylation). Hence, option A is correct.