Bromine water is an orange solution of bromine. It becomes colourless when it is shaken with an alkene. Alkenes can decolourise bromine water, but alkanes cannot.

Does ethene Decolourises bromine water?

Ethene decolourises bromine water because ethene is an alkene. And all alkenes and alkynes are unsaturated compounds which decolourise bromine water. On the other hand, ethane being an alkane is a saturated compound which does not decolourise bromine water.

Does toluene give bromine water test?

When toluene and a bromine solution react, there is no reaction. That is, the solution turns a yellow/brown colour, the same as the bromine solution.