We are given three test tubes each with a different concentration of glucose in it.  The best chemical test to determine which one is the most concentrated would be to add a solution of KMnO4 (potassium permanganate) in acidic solution (such as HCl) to a small sample from each tube.  KMnO4 is a purple solution that turns colorless as it reacts to oxidize glucose in solution.  So take a small sample (say about 1 mL) from each of the tubes and measure the amount of a solution of acidic KMnO4 that is needed to be added to each sample to keep the purple color from disappearing.  The most concentrated sample will require the most KMnO4 to be added to oxidize all of the glucose present.