Iodine solution is added to a cake solution. The color changes to purple. Based on this result, what biological molecules are present in the cake solution?

Starch

Explanation:

The cake solution contains starch. Starch is a mixture of amylose and amylopectin. Amylose results in purple-deep blue color when it comes in contact with iodine. In absence of starch, this tri iodide anion solution has brown color. When starch is added, they both form a charge transfer complex by slipping of iodine molecule inside amylose coil which results in purple-blue black color. Iodine reagent is made by dissolving iodine in aqueous solution of potassium iodide. Color intensity decreases with increasing temperature, low pH and in presence of organic solvents.

starch, because it's reacts with iodine forming a purple solution and it is present in cake