Unsaturated compounds can be identified by their reaction with which of the following?

Unsaturated compounds, which contain carbon-carbon double or triple bonds, can be identified by their ability to react with bromine solution. This is known as a bromination reaction. When bromine, which is a reddish-brown liquid, is added to an unsaturated compound, the double or triple bonds in the molecule react with bromine to form a saturated compound. As a result of this reaction, the reddish-brown color of the bromine solution disappears, indicating the presence of unsaturation in the compound. This color change is a clear and straightforward visual test for unsaturation.

In contrast, hydrochloric acid, water, and sodium chloride do not specifically indicate the presence of unsaturation. Hydrochloric acid typically reacts with alkenes but does not provide a clear test for unsaturation, and water can react with certain unsaturated compounds under specific conditions without clearly demonstrating the unsaturation. Sodium chloride is not generally involved in reactions that would help identify unsaturation in organic compounds. Thus, bromine solution stands out as the most reliable option for indicating unsaturation in organic chemistry.