WAEC Chemistry 2022 Paper

Concept:Alkenes react rapidly with bromine because of the presence of a carbon-carbon double bond, which undergoes electrophilic addition.Explanation:Bromine adds quickly to alkenes because the electron-rich $\mathrm{C}=\mathrm{C}$ bond attacks the bromine molecule.The red-brown color of bromine disappears almost immediately when it is added to an alkene solution.This rapid decolorization is a standard qualitative test for unsaturation.The reaction occurs readily at room temperature without any catalyst or light.Benzene does not react rapidly; it needs a catalyst for substitution.Hexane is a saturated alkane and reacts with bromine only slowly in sunlight.Hexanol has an $-\mathrm{OH}$ group but no double bond, so it does not react rapidly with bromine.Therefore, among the given compounds, only hexene contains the $\mathrm{C}=\mathrm{C}$ double bond needed for a fast reaction with bromine.Answer:$\mathrm{C.}$ Hexene.