What color does distilled water turn in a biuret test?

In a biuret test, the presence of peptide bonds in proteins is detected by a color change when a reagent is added. Distilled water, which does not contain proteins or peptides, does not react with the biuret reagent. Therefore, it maintains its original color, which is light blue. The biuret reagent itself is blue due to its copper sulfate content, and when no proteins are present, it retains this light blue hue.

The other color options indicate the presence of proteins: violet suggests a high concentration of proteins, while green might indicate a lower concentration. Clear would imply a lack of the reagent itself or a complete absence of any color change, which is not typical for a biuret test. Thus, the correct answer reflects the expected observation when testing distilled water, confirming that it remains light blue due to the absence of protein content.