While using biuret reagent, you test not only the mystery food sample, but also gelatin and water. which solution acts as a positive control?

Answer: gelatin

Biuret reagent is used to detect peptide bond of a substance, which will be found when protein is present. The positive control for the reagent should be the food that known to have protein. Gelatin has high protein thus, it becomes positive control. Water has no protein so it will be a negative control.