During the bromine water test, what happens to the bromine species?

• A. It is reduced to bromide ions
• B. It is oxidized to bromate
• C. It remains unchanged
• D. It evaporates

Answer: (A)

When bromine water is used to test for unsaturation, the bromine molecules react with a carbon–carbon double bond by adding across it. In this process, the bromine is consumed and gains electrons, so it is reduced from Br2 to bromide ions (Br-). That reduction removes the orange-brown color of bromine from the solution, giving decolorization. The other possibilities don’t fit this test: bromine isn’t acting as an oxidizing agent to form bromate under these conditions, it isn’t left unchanged, and it doesn’t simply evaporate—the visible change comes from the bromine being reduced as it adds across the double bond.