Which of the following reagents cannot distinguish between glucose and fructose?

All of these

The answer is (4) all of these.

Tollen's reagent, Fehling's solution, and Benedict's solution are all used to test for reducing sugars. Reducing sugars have an aldehyde or ketone group that can be oxidized by these reagents. Glucose and fructose are both reducing sugars, so they will all react with these reagents. Therefore, these reagents cannot be used to distinguish between glucose and fructose.

The only reagent that can distinguish between glucose and fructose is Seliwanoff's reagent. Seliwanoff's reagent is a more specific test that reacts with fructose but not glucose.