Question

why benzene not give bromine water test

Answer 1

unsaturated compounds decolourisebromine. Benzene has no double bonds, however benzene has a ring of delocalised electrons for that reasonbenzene is less reactive.

Answer 2

Unsaturated compounds decolorise bromine as benzene has no double bonds but has a ring of delocalised electrons and thus it is less reactive and hence doesn't give bromine water test.
Hope you understood