Glucose and fructose are both C₆H₁₂O₆ but differ in functional groups — JEE Chemistry

• Glucose is an aldohexose (contains –CHO aldehyde group) → reduces Tollens' reagent directly.

• Fructose is a ketohexose (contains –CO– ketone group) → normally ketones don't reduce Tollens'. However, fructose is an $\alpha$-hydroxy ketone. In basic medium (Tollens'), it isomerises to glucose and mannose via enediol intermediate.

$$Fructose \xrightarrow{OH^-} Enediol \rightarrow Glucose + Mannose$$

$$Both give silver mirror test; fructose due to enolization in base$$