Starch is a mixture of two components, a water-soluble component amylose (15-20%) and a water-insoluble component amylopectin (80-85%). The aqueous solution of amylose gives a blue colour with iodine solution due to the formation of:

• A. amylose iodide
• B. amylose iodate
• C. inclusion complex
• D. amylose tetraiodide complex

When starch is mixed with iodine solution, the blue color that appears is due to the formation of an inclusion complex. This occurs specifically with the amylose component of starch. The iodine molecules fit into the helical structure of amylose, resulting in the characteristic blue color. Therefore, the correct answer is:

Correct Answer

C. inclusion complex

Understanding the Components

• Amylose: A linear polymer that is soluble in water.
• Amylopectin: A branched polymer that is not soluble in water.

Why the Blue Color?

The interaction between iodine and amylose creates a stable complex, which is visually identifiable as a blue color. This reaction is often used in laboratory settings to test for the presence of starch.