At how many points along the electron transport chain is free energy used to transport hydrogen ions across the membrane?

1. Electrons are passed through a series of redox reactions along the chain. 2. A small amount of free energy is used at three points to transport hydrogen ions across a membrane. 3. That transport contributes to the gradient used in chemiosmosis. 4. The electrons themselves gradually lose energy as they move down the chain. 5. Counting four points by matching one pump to each complex is the trap, since not every complex pumps. 6. The end products of the whole chain are water and adenosine triphosphate. _Source: OpenStax Biology (1st ed., CC BY 4.0), Ch 7 "Cellular Respiration", section 7.4 Oxidative Phosphorylation_