If a few drops of iodine solution were added to rice water and the solution turned blue-black in color, this indicates that rice water contains starch.
Explanation: Iodine solution is a common test for the presence of starch; when it reacts with starch, it produces a blue-black color.
Why other options are incorrect:
A. complex proteins:
Proteins do not react with iodine solution in the same way that starch does. Complex proteins, also known as polypeptides, are chains of amino acids linked together by peptide bonds. These bonds are not susceptible to the color change induced by iodine.
B. simple proteins:
Simple proteins are individual polypeptide chains. Similar to complex proteins, they do not react with iodine solution.
C. fats:
Fats, or lipids, are composed of triglycerides and fatty acids. Iodine does not react with fats either. The reaction with iodine is specific to the carbohydrate starch.