Answer;
8 kilo calories/mole.
Approximately 8 kilo calories/mole more free energy is supplied to the electron transport chain by NADH than by FADH2.
Explanation;
-An NADH molecule produces 3 ATP during the ETC (Electron Transport Chain) with oxidative phosphorylation because NADH gives up its electron to Complex I, which is at a higher energy level than the other Complexes.
-An FADH2 molecule produces 2 ATP during the ETC because it gives up its electron to Complex II, bypassing Complex I.