This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Biochemistry
Which of the following vitamin is used in the electron transport chain 
Select and explain. 
A. Thiamine, B. Riboflavin, C. Nicotinic acid, D. Vitamin B12
B: Riboflavin
Answer: B: Riboflavin 
Explanation: This question is a tricky one.

Both nicotinic acid and riboflavin are important for ETC.
NADH (derivative of nicotinic acid) and FADH2 (derivative of riboflavin) serve as the substrates for ETC by donating their electrons. They are not the part of ETC as such.
FMN (derivative of riboflavin) is a part of ETC; it is a coenzyme component of complex I (NADH - COQ reductase).

So, the best answer here is riboflavin.