What is observed when bromine water is mixed with an alkene?

When bromine water is mixed with an alkene, the solution turns colorless due to a chemical reaction. Alkenes contain carbon-carbon double bonds, which are reactive sites that can undergo addition reactions. Bromine, being a diatomic halogen, reacts with the double bond of the alkene to form a dibrominated compound, effectively breaking the double bond.

This reaction reduces the bromine concentration in the solution, leading to the loss of the characteristic reddish-brown color of bromine water. The color change from orange-brown to colorless is a clear demonstration of the alkene's presence and the reactivity characteristic of alkenes.

In contrast, the other options do not accurately represent the behavior of bromine water with alkenes. For instance, if bromine water were to remain orange, it would indicate that no reaction occurred, which is not the case with alkenes. Similarly, turning yellow or becoming cloudy does not accurately describe the observed color change; cloudiness typically arises from a suspension or emulsification, but in the context of adding bromine to alkenes, the expected outcome is a colorless solution.