Which one given below is a non-reducing sugar?

Solution & Explanation

\textbf{Answer:} (D) Sucrose has no free anomeric carbon, so it is non-reducing. \textbf{Solution:} In sucrose ($\mathrm{C}{}_{12}\mathrm{H}{}_{22}\mathrm{O}{}_{11}$) the glycosidic linkage joins the anomeric carbon of glucose (C-1) to the anomeric carbon of fructose (C-2), so no free hemiacetal/hemiketal ($-\mathrm{OH}$ on anomeric C) group remains — hence it is non-reducing. Maltose and lactose each retain one free anomeric carbon, and glucose has a free $-\mathrm{CHO}$; all three are reducing sugars.