Some crushed boiled rice is put in water in a test-tube ans a few drops of dillute 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 blu-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 X?

Answer

**Step-by-Step Solution:**

1. **Understanding the Experiment**: The experiment involves crushed boiled rice mixed with water, followed by the addition of dilute iodine solution. The blue-black color indicates the presence of a specific substance in the rice.

2. **Identifying Substance X**: The blue-black color produced when iodine is added suggests that the substance present in the rice is starch. Iodine reacts with starch to produce this characteristic color.

3. **Effect of Saliva**: When saliva is added to the crushed boiled rice and water mixture before adding iodine, no blue-black color is produced. This indicates that the starch (substance X) has been converted into another substance (substance Y) by the action of saliva.

4. **Role of Saliva**: Saliva contains enzymes, such as amylase, which break down starch into simpler sugars (like maltose). Since maltose does not react with iodine to produce a blue-black color, the absence of color confirms that starch has been converted.

5. **Conclusion**: Therefore, the substance X present in rice is starch.

**Final Answer**: X is starch.

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