Iodine solution is prepared by dissolving iodine in a solution of potassium iodide. This iodine reagent is amber-yellow colored. When this iodine solution is added to starch solution which is a polysaccharide, the yellow colored reagent changes to blue-block color. This color change is due to the formation of a charge transfer complex between starch and the triioidide present in iodine solution. So, the correct answer is d. the presence of starches or complex carbohydrates
