This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Respiratory Chain, Subject name: Biochemistry
In ETC at which complex ATP is not formed - 
Select and explain. 
A. NADH CoQ reductase, B. Succinate CoQ reductase, C. CoQ-cytochrome-C reductase, D. Cytochrome C oxidase
B: Succinate CoQ reductase
Answer: B: Succinate CoQ reductase 
Explanation: Ans. is 'b' i.e., Succinate CoQ reductase Complex (I-IV) & Sites (I-III of ATP formation) in ETCComplex I: NADH CoQ-reductasePermit ATP formation (Site I)Act as proton pumpComplex II: Succinate CoQ reductaseNo ATP formComplex III; CoQ - cytochrome - C reductasePermit ATP formation (Site II)Act as proton pumpComplex IV: Cytochrome C oxidasePermit ATP formation (Site III)Act as proton pump