Sudha took a small amount of an unknown food item in a test tube. Then, she added a few drops of iodine to it. The colour of the unknown food item changes to blue-black.
The change in colour of the food item to blue-black indicates the presence of
Carbohydrates
The change in colour of the food item to blue-black indicates the presence of starch in the food item. Starch is a carbohydrate. Thus, the change in colour indicates the presence of carbohydrates in the food item.