Which statement best describes the substitution reaction described in the material?

Which statement best describes the substitution reaction described in the material?

• A. Reactants put under a bright light with bromine water.
• B. Reactants are heated with oxygen.
• C. Reactants are cooled to 0°C.
• D. Reaction produces hydrogen gas.

Answer: (A)

This question tests how halogen substitution of an alkane occurs when light is involved. In a substitution with bromine, bright light breaks Br–Br bonds to form bromine radicals. These radicals remove a hydrogen from the hydrocarbon, creating a carbon radical, which then reacts with Br2 to form the brominated product and regenerate another Br• radical. The presence of bromine water provides the bromine source, and the light is the energy that starts the radical chain. This describes a substitution process, not oxidation, not simple cooling, and not hydrogen gas production. The other options describe conditions that would lead to burning/oxidation (hot oxygen), no reaction (cooling), or a different type of reaction that releases H2, none of which match the described substitution mechanism.

This question tests how halogen substitution of an alkane occurs when light is involved. In a substitution with bromine, bright light breaks Br–Br bonds to form bromine radicals. These radicals remove a hydrogen from the hydrocarbon, creating a carbon radical, which then reacts with Br2 to form the brominated product and regenerate another Br• radical. The presence of bromine water provides the bromine source, and the light is the energy that starts the radical chain. This describes a substitution process, not oxidation, not simple cooling, and not hydrogen gas production. The other options describe conditions that would lead to burning/oxidation (hot oxygen), no reaction (cooling), or a different type of reaction that releases H2, none of which match the described substitution mechanism.