Which of the following vitamin is used in the electron transport chain

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.