Final answer:
The correct answer is option B. When dilute iodine solution is added, chewed bread will turn blue-black due to the presence of starch, despite the beginning of the digestion process which breaks down starch into simpler sugars.
Step-by-step explanation:
The student's question is about identifying which among the given options will turn blue-black when adding dilute iodine solution. The iodine test is a chemical test for the presence of starch. When iodine is added to a sample containing starch, a chemical reaction occurs that results in a blue-black color. Bread, composed mostly of starch, will turn blue-black upon the addition of iodine solution.
Chewed bread will also turn blue-black since the chewing process does not remove starch; however, it may be less pronounced if digestion has begun, as saliva starts breaking down starch into simpler sugars.
Grapes, which contain simple sugars like fructose and glucose rather than starch, will not give a blue-black color. Similarly, chewing grapes releases these simple sugars but does not produce starch. Hence, the correct option that will turn blue-black on adding dilute iodine solution is B. Chewed bread.