Question 14
A drop of iodine solution is added to a food that contains starch. What is seen?
The right answer is the one marked above.
A blue-black colour, tending towards purple. That is the test for starch: crush the food with water in a test tube, add one drop of iodine solution, and read the colour.
The other three belong to other tests — brick red to Benedict's for sugars, rose-purple to Biuret for proteins, and a red oil layer to Sudan III for lipids.