Question

Which among the following will turn blue-black on adding dilute iodine solution?

• A. Bread
• B. Chewed bread
• C. Grapes
• D. Chewed grapes

Answer 1

The correct option is A Bread

• Bread contains starch, while grapes contain sugar. A blue-black colour is formed when iodine solution is added to starch. As iodine can form complex with starch. So, a blue-black colour is seen in case of bread.
• Grapes contain sugar. Sugar cannot form complex with iodine. So, no blue-black colour is seen.
• Upon chewing, the food gets mixed with saliva. Saliva contains the enzyme amylase that breaksdown starch into sugars. So, no blue black colour is seen.