This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: ETC, Subject name: Biochemistry
Which couple has minimum redox potential? 
Select and explain. 
A. NADP+/NADPH, B. CoQ-CoQ H2, C. FAD/FADH2, D. NAD+/NADH
D: NAD+/NADH
Answer: D: NAD+/NADH 
Explanation: NAD+/NADH has minimum redox potential NADH has minimum redox potential Oxygen has maximum redox potential As you go ahead in ETC , redox potential increases i.e Complex I < Complex II < Coenzyme Q < Complex III Fig.: A flowcha showing redox pairs with increasing redox potential. Redox Pair consists of two components- one is oxidized and other is reduced during electron transfer