If bromine water shows no color change with a sample, what does this indicate?

• A. There is no carbon-carbon double bond present
• B. The sample contains an alkene but does not react
• C. Bromine water was not added correctly
• D. The sample is pure water

Answer: (A)

The test uses bromine water to probe for unsaturation, specifically carbon–carbon double bonds. Bromine adds across a C=C bond in alkenes, which uses up the bromine and makes the solution lose its orange-brown color. If there’s no color change, there isn’t a C=C double bond for bromine to add to, so the sample is saturated and contains no carbon–carbon double bond.

So the best interpretation is that the sample lacks C=C bonds. If there were an alkene present, the bromine water would decolorize. The idea that the alkene does not react would contradict how this test works, and while a procedural error could explain a lack of change, the straightforward chemical reading is an absence of unsaturation. Saying the sample is pure water is a possible specific case, but the general conclusion about structure is the absence of a carbon–carbon double bond.