For each FADH2 that supplies electrons to the electron transport system, 2ATPs are synthesized. For each NADH that supplies electrons to the electron transport system, 3 ATPs are synthesized.
Explanation:
Both FADH2 and NADH are you reducing equivalents in that they give off electron in terms of hydrogen atom or a hydride ion.
Thus, in the inner membrane of the mitochondria where electron transport occurs, FADH2 gives off its hydride ion yielding 2 ATP molecules; while NADH gives off its hydride ions to yield 3 ATP molecules
