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

Buiret Solution is specifically designed to test for the presence of proteins. It contains copper sulfate, which reacts with peptide bonds found in proteins. When proteins are present, the solution changes color, typically turning from blue to purple, indicating a positive result. This is due to the formation of a complex between the copper ions in the Buiret reagent and the peptide bonds during the reaction.

In contrast, the other options are designed for different macromolecules or functions. Benedict's Solution is primarily used to test for reducing sugars, where a color change occurs in the presence of simple carbohydrates. Iodine Solution is used to detect the presence of starch, turning blue-black when starch is present. Litmus Solution serves as an acid-base indicator and does not test for macromolecules but rather indicates pH changes. Therefore, Buiret Solution is the correct choice for identifying proteins.