Question

A few drops of iodine solution were added to rice water. The solution turned blue-black in colour. This indicates that rice water contains

• A. complex proteins
• B. simple proteins
• C. fats
• D. starch

Answer 1

The correct option is D

starch

The correct option is (D).

Explanation of the correct option:

1. A solution of iodine and potassium is added to a starch-containing substance instead of molecular iodine because molecular iodine is not soluble in water.
2. Starch is a polymer of amylose and amylopectin, of which amylose is responsible for the blue colour of the reaction.
3. The reaction proceeds as follows:- I₂ + I⁻→ I₃⁻– + starch (dark blue colour)
4. In the absence of starch solution, remains as light brown colour which is the colour of iodine solution.

Final answer: A few drops of iodine solution were added to rice water. The solution turned blue-black in colour. This indicates that rice water contains starch.