A sample of propene is mixed with bromine water at room temperature in the dark. A second sample is mixed in the same way while exposed to ultraviolet light. Which observation is correct?
Only the illuminated mixture turns colourless because ultraviolet light is needed.
Both mixtures turn colourless because ultraviolet light is not needed.
Only the mixture kept in the dark turns colourless; the illuminated mixture stays orange.
Both mixtures stay orange because a catalyst is needed.