Question 20
Boojho took some grains of boiled rice in test tube ‘A’ and Paheli took boiled and chewed rice in test tube ‘B’. Both of them poured 1 - 2 drops of iodine solution into the test tube and observed the colour change. What colour change would they have observed? Give reasons for your answer.

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Solution

The iodine test is carried out to detect the presence of starch in a food item. If starch is present in a food item, the food item will turn blue-black in colour with the addition of iodine.

In test tube ‘A’, blue-black colour appears because of the presence of starch.

In test tube ‘B’, the colour of iodine will not change because the digestion of starch into sugars took place.

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Q. Boojho took some grains of boiled rice in test tube ‘A’ and Paheli took boiled and chewed rice in test tube ‘B’. Both of them poured 1 – 2 drops of iodine solution into the test tube and observed the colour change.
What colour change would they have observed? Give reasons for your answer.

Q. Case: Observe the image given below. There are two test tubes (i) and (ii). Test tube (i) contains a starch solution, while test tube (ii) contains starch solution and saliva. Both the test tubes are kept undisturbed for about 20 min. Later, dilute iodine solution (brown in colour) was added to both the test tubes.

We have two test tubes here, X and Y. X contains boiled rice and Y contains boiled rice that has been completely chewed on. Which one is more likely to turn blue-black on adding an iodine solution?

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Question 20

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Q. Rima was given two test tubes labelled A and B. When she dipped an iron nail in both the test tubes, she observed that the colour of the solution changed as shown in the image given below. Identify the solutions in test tubes A and B.

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