Multiple choice general knowledge science & technology Which food stuff turns blue-black when brought in contact with iodine? Proteins Vitamins Starch Unsaturated Fatty Acids Reveal answer Fill a bubble to check yourself C Correct answer Explanation Iodine solution turns blue-black in the presence of starch, which is a well-known chemical test in biology. Proteins, vitamins, and unsaturated fatty acids do not produce this characteristic color change with iodine.