This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Classification of carbohydrate, Subject name: Biochemistry
Enantiomers are isomers that differ in structure at which carbon : 
Select and explain. 
A. Last Carbon, B. First Carbon, C. Penultimate Carbon, D. Carbonyl Carbon
C: Penultimate Carbon
Answer: C: Penultimate Carbon 
Explanation: Enantiomers have different -H and -OH orientation around the penultimate carbon /2nd last carbon/Reference carbon. E.g-. D-and L-Glyceraldehyde. Also known as Mirror images of each other.