In aerobic respiration, what is the direct source of energy that atp synthase uses to synthesize atp?

For the answer to the question above asking In aerobic respiration, what is the direct source of energy that ATP synthase uses to synthesize ATP?I think this is Proton Gradient. It is the product of the electron transport chain. A higher concentration of protons outside the inner membrane of the mitochondria than inside the membrane is the driving force behind ATP synthesis.

Dis the correct answer thats what i put and it was right 

Yes yes yes very good