Hello,

Iodine solution is used to test leaves for the presence of starch. You need to heat a plant leaf in boiling water for 30 seconds this stops its chemical reactions heat it in boiling ethanol for a few minutes this removes most of its colour. Presence of starch in leaves can be tested by process called iodine test. Iodine turns starch solution into blue-black colour. Pour few drops of dilute iodine solution on the boiled leaf. The leaf becomes blue-black which proves the presence of starch in it.