Why is iodine solution used to test starch?

Iodine solution is used to test starch because it reacts specifically with amylose, a component of starch. When iodine molecules enter the spiral structure of amylose, they form a complex that produces a blue-black colour, indicating the presence of starch.

This reaction is simple, quick, and reliable, making the iodine test one of the most common methods for detecting starch in food samples during school science experiments. If starch is absent, the iodine solution remains brown or yellow-brown.