Energy and Metabolism

ID #2338

In biological reactions, electrons are transferred via hydrogens. When reducing FAD, how many electrons and/or protons are transferred? Incorrect: 4 protons Incorrect: 4 electrons Incorrect: 1 proton Incorrect: 3 electrons and 1 proton Correct: 2 electrons Why is it that 2 electrons are transferred and not 2 electrons and 2 protons? Since 2 Hydrogens are added.

You are correct that FAD is reduced to FADH2 when it gains two hydrogen atoms. Since a hydrogen is an electron and a proton, FAD gets two electrons and two protons when it is reduced. 
The question stem asked you to decide how many electrons "and/or" protons are transferred. "And/or" means the correct answer could discuss both electrons and protons, or just electrons, or just protons. The correct answer from your options simply discussed the number of electrons and said nothing about the number of protons. 

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