Let's analyze each compound:
Phenol:
Phenol contains an electron donating group (OH) attached to a benzene ring, activates the ring toward electrophilic substitution. Phenol readily undergoes electrophilic substitution reactions with bromine, leading to decolourisation.
Styrene:
Styrene contains a vinyl group (CH=CH2) attached to a benzene ring. The alkene part of styrene will readily react with bromine water by addition reaction.
Aniline:
Aniline also contains an activating amine group (NH2) attached to a benzene ring. It readily undergoes electrophilic substitution reactions with bromine, leading to decolourisation.
Cyclohexane:
Cyclohexane is a saturated cyclic alkane. It lacks double or triple bonds and isn't readily susceptible to electrophilic attack (it would require much higher temperatures and/or UV light to react). So Cyclohexane does not decolourise bromine water under normal conditions.
Therefore, cyclohexane does not decolourise bromine water.
The compound that does not decolourise bromine water is (4) Cyclohexane.
Consider the following two reactions A and B: 
The numerical value of [molar mass of $x$ + molar mass of $y$] is ___.
Which one of the following graphs accurately represents the plot of partial pressure of CS₂ vs its mole fraction in a mixture of acetone and CS₂ at constant temperature?

Consider the following reaction sequence: 
Given: Compound (x) has percentage composition \(76.6%\ \text{C}\), \(6.38%\ \text{H}\) and vapour density \(=47\). Compound (y) develops a characteristic colour with neutral \(\mathrm{FeCl_3}\) solution. Identify the {INCORRECT statement.}
What is Microalbuminuria ?
The output (Y) of the given logic implementation is similar to the output of an/a …………. gate.