The iodine changes color in the presence of
a sugar
a protein
a hydrocarbon
a starch

A starch

Explanation:

Many food products contain a carbohydrate that is called as starch like rice, corn, potatoes, pasta and grains. Iodine solutions can be used for testing the food samples that are expected to consist of starch. In the presence of starch the iodine solution changes it's color from brown to blue-black to purple. This solution is a reliable source of identification of starch.

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