Final answer:
Solution X is starch, which turns blue-black when iodine is added due to its amylose content. Solution Y is amylase, which breaks down starch into smaller molecules that react with iodine to give an orange-brown color. The correct answer is Option C: X: starch, Y: amylase.
Step-by-step explanation:
When solution X is tested with iodine, a blue-black color indicates the presence of starch. This is because starch, a mixture of the polymers amylose and amylopectin, forms a complex with iodine that is blue-black. Specifically, it is the amylose in starch that traps iodine molecules within its helical structure, leading to the formation of this colored complex.
Solution X initially gave a blue-black color with iodine, which changed to an orange-brown color after solution Y was added and the mixture was incubated. This color change suggests a chemical reaction. The enzyme amylase is known to break down starch into smaller sugar molecules that do not form the blue-black complex with iodine. The disappearance of the blue-black color and the appearance of the orange-brown color indicates the breakdown of starch into smaller molecules that give a different coloration when interacting with iodine. Therefore, solution Y is likely an amylase solution, capable of hydrolyzing starch into simpler sugars which do not form the characteristic blue-black complex with iodine.
Thus, the correct answer to the question is Option C: X: starch, Y: amylase.