In oxidative phosphorylation, what are the immediate products of the electron transport chain (ETC) before ATP synthase acts?

• A. Net production of $C_{O}2$ and $FADH2$
• B. Direct synthesis of ATP from $ADP$ and $P_i$ in the mitochondrial matrix
• C. Oxidation of $NADPH$ to $NADP+$ and production of $O_2$
• D. A proton gradient across the inner mitochondrial membrane and reduced oxygen as $H_{2}O$

Answer: (D)