Question

When starch is treated with iodine solution, its color changes to
(A) Yellow
(B) Red
(C) Blue-black
(D) Green

Answer 1

Hint: The starch and iodine test is to test the presence of carbohydrates in the plants which upon reaction gives a dark-colored solution.

Complete answer:
Starch is tested to find the presence of starch in the plant parts. The starch is the reserve food material stored in plants mainly present in the leaves. When the starch comes in contact with iodine it will show blue-black color. This blue-black color is the color of the starch iodide complex.

Additional Information:
When the iodine solution and potassium iodide solution are mixed in water, they will produce a brown color and after the addition of starch in that solution, the color will turn deep blue. The starch iodide complex absorbs visible light depending upon the energy intensity and thus giving a blue-black color. If the food does not contain starch, it gives a yellowish color.
The presence of starch in the leaves of the plants tells whether the photosynthesis has occurred or not. Starch is a carbohydrate that is made up of several molecules of glucose. It is the most common type of carbohydrate which is present in human diets and staple foods like potatoes, rice, maize, etc. They are the source of energy in green plants while iodine is a chemical element that is the primary element used in nutrition. It is useful in the synthesis of thyroid hormones. The deficiencies of iodine may lead to various serious disabilities.

Correct answer is Blue-black

Note: The word "starch" is derived from the German word having various meanings "strong, stiff, strengthen, stiffen". The term has a Greek origin for starch, "amylon" which means "not milled". The iodine element was first discovered in 1811 by the French chemist Bernard Courtois and it was named after two years later by Joseph Louis Gay-Lussac, after the Greek meaning "violet-colored". It is largely produced in countries like Chile and Japan.