Question

Why do unsaturated hydrocarbons decolourise bromine water

Answer 1

Explanation:

It's not just Cyclohexene, but ALL Alkene molecules that decolourise when they react with Bromine water. Alkenes contain a C=C double bond and thus we call them "unsaturated hydrocarbons". Bromine (Br2) breaks this C=C double bond and attaches itself to the Alkene molecule, forming an Alkane.

Answer 2

Answer:

Unsaturated means double or triple bonded compounds of carbon. So, in the presence of an attacking reagent like bromine, the double or triple bond breaks making the compound unstable. If you will make it to react with bromine then firstly the bond will break and then bromine will get attach to each carbon end.