Answer:
Starch
Step-by-step 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.