In the bromine water test, what is the role of bromine?

• A. Bromine adds across the double bond
• B. Bromine acts as a solvent
• C. Bromine acts as a catalyst
• D. Bromine breaks the double bond into two fragments

Answer: (A)

Bromine in the bromine water test behaves as an electrophile that adds across a carbon–carbon double bond. The C=C bond is electron-rich, so it polarizes Br2 and causes each bromine atom to attach to a different carbon, converting the alkene into a dibromoalkane. As this addition happens, the bromine is consumed and the orange-brown color of bromine water fades, giving a decolorized solution. This is why bromine’s role is described as adding across the double bond, not acting as a solvent or a catalyst, and not causing cleavage into fragments.