Question

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

Answer 1

A host-guest addition compound is used. The question is from disaccharides and polysaccharides. The above question is from the chapter Biomolecules of organic chemistry. Process of reaction of amylose with iodine is used.

Complete step by step answer:
The room accessible inside the host molecule's crystal lattice, i.e., amylose, is in the form of tunnels. The tunnels' scale is such that the guest molecules, i.e., iodine molecules, can be easily accommodated to form an external compound called the inclusion complex.
The blue color, however, disappears on heating and also reappears on cooling.
In the case of the option A that is amylose iodine, the solution's color turns out to be a deep blue-purple colour solution that does not match with this question.
In the case of options B, that is amylose iodate that can surely not be the answer cause the compound given cannot be formed with amylose and amylopectin.
In option D, the amylose tetraiodide complex is the hydrophobic channel that does not meet our question.

**Hence the correct answer is C. inclusion complex

Note:**
The knowledge of polysaccharides is an essential part of organic chemistry, as many questions from this section of organic chemistry have already appeared. Students should know the organic chemistry reaction and must practice it.