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Which one of the following compounds does not decolourize bromine water?
A
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B
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C
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D
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Explanation
Cyclohexane is a saturated cycloalkane that does not react with bromine water. Phenol, aniline, and styrene rapidly decolourize bromine water.
Detailed Solution
Bromine water is decolourized by unsaturated hydrocarbons via electrophilic addition (e.g. styrene adds $\text{Br}_2$ across its vinyl double bond) or by strongly activated aromatic rings via rapid electrophilic aromatic substitution (e.g. phenol forms 2,4,6-tribromophenol white precipitate, and aniline forms 2,4,6-tribromoaniline). Saturated alkanes like cyclohexane lack both unsaturation and activation, and thus do not decolourize bromine water in the absence of UV light.