What color is bromine water at the start of the test?

• A. Orange-brown
• B. Colorless
• C. Blue
• D. Green

Answer: (A)

The main idea here is that bromine water shows the color of dissolved bromine. At the start, bromine water is orange-brown because Br2 in water gives a reddish-orange solution. This color is visible before any reaction takes place. If you shake it with an alkene, the bromine adds across the double bond and the solution decolorizes, turning colorless as Br2 is consumed. The other color options don’t fit bromine water’s initial state, since colorless would mean no bromine is present and blue or green are typical of different solutions, not bromine water.