What test is commonly used to detect carbohydrates?

The iodine test is specifically designed to detect the presence of starch, which is a polysaccharide carbohydrate. In this test, iodine forms a blue-black complex when it interacts with the helical structure of starch molecules. This distinctive color change is a clear indicator of the presence of starch in the sample being tested.

In contrast, other tests listed serve different functions: the Benedict's test is used primarily for detecting reducing sugars such as glucose and fructose, the biuret test is utilized to identify proteins by detecting peptide bonds, and the litmus test is employed to determine acidity or alkalinity in a solution. Therefore, the iodine test is the most appropriate choice for detecting carbohydrates, specifically starches.