Which of the following substances tests for proteins?

The Biuret Test is specifically designed to identify the presence of proteins. During this test, when a protein is mixed with a Biuret reagent (which contains copper sulfate), a color change occurs, typically turning from blue to purple. This is due to the formation of a complex between the copper ions and the peptide bonds in the protein. The development of this purple color is a clear indicator that proteins are present.

The other tests mentioned are intended for different substances. For instance, the Benedict's Test is used to detect reducing sugars, not proteins. The Iodine Solution tests for starch, resulting in a blue-black color if starch is present. Similarly, the Lipid Test detects the presence of lipids (fats) using a different method, often involving the emulsion test that can result in a cloudy appearance when lipids are present. Each of these tests serves a specific purpose and is tailored to identify particular biomolecules, highlighting the uniqueness of the Biuret Test for protein detection.