Cellulose does not form blue colour with Iodine because
Answer: (C) It does not contain complex helices and hence cannot hold iodine molecules.. Answer: (C) It does not contain complex helices and hence cannot hold iodine molecules.
- A.It is a disaccharide.
- B.It is a helical molecule.
- C.It does not contain complex helices and hence cannot hold iodine molecules.✓
- D.It breakes down when iodine reacts with it.
Correct Answer
(C) It does not contain complex helices and hence cannot hold iodine molecules.
Solution & Explanation
Answer: (C) It does not contain complex helices and hence cannot hold iodine molecules. Solution: The blue colour of the starch-iodine test arises because starch forms helical secondary structures that can trap I2 molecules within the helical portion. Cellulose, although a glucose polymer, does not form these complex helices, so it cannot hold iodine and therefore does not give a blue colour. Option (B) is wrong (cellulose is not described as helical) and (A)/(D) are factually incorrect. NCERT Reference: Ch 9, p.110, line ~41 — "Starch forms helical secondary structures. In fact, starch can hold I2 molecules in the helical portion. The starch-I2 is blue in colour. Cellulose does not contain complex helices and hence cannot hold I2."