Question

which reagents are used in starch test?

Answer 1

Iodine - KI Reagent: Iodine is not very soluble in water, therefore the iodine reagent is made by dissolving iodine in water in the presence of potassium iodide. This makes a linear triiodide ion complex with is soluble. The triiodide ion ion slips into the coil of the starch causing an intense blue-black color.

Answer 2

You can have that a bit backwards. A solution of starch is used to test for iodine, but I suppose you could use iodine to test for the presence of starch.