The product of the reaction between starch and iodine is a blue-black complex. This is a classic chemical test used to detect the presence of starch.

Here's why this happens:

* Starch Structure: Starch is a long chain of glucose molecules linked together. The structure of starch includes helical (spiral) portions.

* Iodine Interaction: Iodine molecules can fit into the helical portions of the starch molecules.

* Color Change: The interaction between iodine and starch creates a complex that absorbs light in the visible spectrum, resulting in the characteristic blue-black color.

Important Note: This is not a chemical reaction in the sense of forming a new compound. It's more of a physical interaction where iodine molecules are trapped within the starch structure.