Consider assembling a microbial fuel cell using an open air cathode and waste water containing organic compounds to be decomposed. Choose one of the following three redox couples, Feredoxin (Fe2+ )/Feredoxin (Fe3+), NAD+ /NADH or FAD/FADH2. Note that NAD is Nicotinamide Adenine Dinucleotide, and FAD is Flavin Adenine Dinucleotide. If one mole of the redox couple is involved in the cell operation, find which redox couple generates the highest energy from the cell, and answer why. Calculate the amount of the generated energy.

Fe3 ⁺ + e ^- --> Fe2 ⁺ -0.42V

O ₂ +4H ⁺ + 4e ^- ---> 2H ₂ O +0.84 V

NAD ⁺ +H ⁺ +2e ^- ?---> NADH -0.32 V

FAD ⁺ +2H ⁺ +2e ^- ? ?---> FADH ₂ -?0.18 V?