We know that the reddish brown colour of bromine solution in carbon tetrachloride is discharged when bromine adds up to an unsaturation site.
Cyclobutane (a) and cyclohexane (c) do not have any π bonds for addition reactions. Hence, they will not decolourise bromine water.
Compound (b) is benzene. Benzene has π electrons that are delocalised over the entire ring. Benzene will not undergo addition reactions since addition reactions will destroy the aromaticity of benzene. Hence, it will not decolourise bromine water.
An alkyne is given in option (d). Since unsaturation is present in but-2-yne, it will decolourise bromine water.
Thus, the compounds given in (a), (b), and (c) will not decolourise bromine water.