Bromine water helps in testing and detecting unsaturated hydrocarbons such as alkene and alkynes.
It is also helpful in testing the bunch of Aldehyde present in any compound.
When we react Bromine water with Alkenes, Bromine water gets decolorized and when it is reacted with saturated hydrocarbons it does not get decolorized.
Therefore, saturated hydrocarbons do not decolorize bromine water.
Example: When propane reacts with Bromine water no reaction is obtained and therefore the bromine water does not decolorize.