Question

take 5 ml of rice gruel in a test tube and add 5 ml of saliva shake it will after sometime add a few drop of iodine solution to it observe the colour change

Answer 1

First:  If you add iodine to the test tube with rice gruel only, the solution will be colored blue-black. This coloration is due to the presence of starch in the rice.

Second: In the solution of rice gruel + saliva, the concentration of starch is expected to decrease over time.

*Saliva has amylase that increases the speed of breaking down starch into simple sugars/monosaccharides.

*Thus, when all of the starch is broke down into simple sugars, the solution after adding iodine will not change color.

Answer 2

As soon as iodine solution is added to the test tube, there is no change in color.

This is particularly because the saliva shake which was added to the tube broke down the starch particles of the rice into the sugars.

As there is starch left, iodine does not change its color.