This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: vitamins, Subject name: Biochemistry
Which Vitamin is involved in Redox reactions? 
Select and explain. 
A. Pyridoxin, B. Biotin, C. Folic acid, D. Riboflavin
D: Riboflavin
Answer: D: Riboflavin 
Explanation: Riboflavin is involved in redox reactions. Co-enzyme Activity of Riboflavin: Riboflavin exists in tissues tightly bound (but not covalently) with enzymes. Enzymes containing riboflavin are called flavoproteins. The two coenzymes are FMN (flavin mononucleotide) and FAD (flavin adenine dinucleotide) (Fig. 34.4). A. FAD Accepts Hydrogen During the oxidation process, FAD accepts two hydrogen atoms from substrate. In turn, FAD is reduced to FADH2. The two nitrogen atoms of the isoalloxazine nucleus accept the hydrogen atoms Reference: Vasudevan Textbook of Biochemistry pg no. 393