Some crushed boiled rice is put in water in a test-tube and a few drops of dilute iodine solution are added to it. A blue-black colour is produced which shows the presence of X in rice. If, however, the crushed boiled rice and water are first warmed with saliva for some time and then dilute iodine solution in added, then no blue-black colour is produced. This shows that saliva converts X into product Y which does not produce blue-black colour with dilute iodine solution.
Name Y?

Answer

**Step-by-Step Solution:**

1. **Understanding the Experiment**: The experiment involves crushed boiled rice mixed with water and iodine solution. Initially, a blue-black color is produced, indicating the presence of a substance (X) in the rice.

2. **Identifying Substance X**: The blue-black color indicates that substance X is starch. Iodine solution reacts with starch to produce a blue-black color.

3. **Introducing Saliva**: When the crushed boiled rice and water are warmed with saliva before adding the iodine solution, no blue-black color is produced.

4. **Analyzing the Effect of Saliva**: The absence of the blue-black color after adding iodine suggests that saliva has changed substance X (starch) into another substance (Y) that does not react with iodine.

5. **Determining Substance Y**: Saliva contains enzymes that break down starch into simpler sugars. The primary product formed from the breakdown of starch is maltose, which is a disaccharide sugar.

6. **Conclusion**: Therefore, the substance Y, which does not produce a blue-black color with iodine, is a simple sugar, specifically maltose or glucose.

**Final Answer**: Y is a simple sugar (maltose or glucose).

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