Question

Some pieces of potato fries are placed on three plates as shown below. In plate A, water is added. In plate B, saliva is added and mixed thoroughly. Nothing is done to the fries in plate C.

The plates are undisturbed for 1 hour. A few drops of iodine is added to each plate. In which plate will the iodine remain brown?

• A. Both B and C
• B. B only
• C. Both A and B
• D. A only

Answer 1

The correct option is B B only

Iodine remains brown in plate B. Saliva will convert starch to glucose. Glucose does not give any colour to iodine. So, iodine remains brown in plate where fries are mixed with saliva. A blue-black color will result in plate A and C due to the presence of starch in both cases.