Which solution is used to test for the presence of proteins?

The Biuret solution is specifically designed to test for the presence of proteins. This solution contains copper sulfate, which reacts with peptide bonds in proteins to produce a color change, typically from blue to violet. This reaction occurs because the copper ions from the Biuret reagent complex with the nitrogen atoms in the peptide bonds, indicating the presence of proteins in the sample being tested.

The other solutions mentioned serve different purposes: Iodine solution is used to test for starch, Benedict's solution is used for detecting reducing sugars, and Sudan III solution is utilized for identifying lipids. Each of these tests relies on distinct chemical reactions related to the macromolecules they target, demonstrating the specificity of biochemical assays in laboratory settings.