Fructose and glucose can be distinguished by:

Step 1: Monosaccharide Classification — Glucose is an aldose (with an aldehyde group) and fructose is a ketose (with a keto group).

Step 2: Selecting the Test — Tests like $\text{Fehling's}$ or $\text{Benedict's}$ react with both reducing aldoses and ketoses. $\text{Seliwanoff's test}$ is specifically used to distinguish them.

Step 3: Observation — In $\text{Seliwanoff's test}$, the keto-fructose reacts much faster under acidic conditions to give a cherry-red color, whereas aldo-glucose responds much more slowly.

Remember: Resorcinol in concentrated $\ce{HCl}$ is the key constituent of $\text{Seliwanoff's reagent}$.