Used as a sensitive test for oxidizing agents, particularly free halogens like chlorine, bromine, and iodine. When exposed to these substances, the solution turns deep blue due to the formation of the starch-iodine complex. Commonly used in water testing to detect residual disinfectants, in titrations involving iodine, and in educational experiments to demonstrate redox reactions. Also applied in environmental monitoring and industrial processes where rapid visual detection of oxidation potential is needed.