Which one of the following compounds does NOT decolourize bromine water? (1) cyclohexane; (2) phenol (C6H5OH); (3) styrene (C6H5-…

Question

Which one of the following compounds does NOT decolourize bromine water? (1) cyclohexane; (2) phenol (C6H5OH); (3) styrene (C6H5-CH=CH2); (4) aniline (C6H5-NH2).

1. A. Cyclohexane (Correct answer)
2. B. Phenol
3. C. Styrene
4. D. Aniline

Correct Answer

Option A — Cyclohexane

Detailed Solution & Explanation

The correct answer is cyclohexane.

Key Points

• Bromine water is decolourised either by addition across a C=C (unsaturation) or by electrophilic substitution on an activated ring.
• Styrene adds Br$_2$ across its double bond; phenol and aniline are strongly activated rings that undergo bromination (giving tribromo products) — all three decolourise bromine water.
• Cyclohexane is a saturated alkane with no reactive site, so it does not decolourise bromine water.