Final answer:
When starch reacts with iodine, it forms a blue-violet color due to the formation of the amylose-iodine complex.
Step-by-step explanation:
When starch reacts with iodine, it forms a blue-violet color due to the formation of the amylose-iodine complex. This color test is sensitive enough to detect even minute amounts of starch in solution. Therefore, the correct answer is A) Starch turns blue.