Why is UV light necessary in the reaction between alkanes and bromine water?

The reaction between alkanes and bromine water involves a radical substitution mechanism, which requires energy to initiate the process. UV light serves as a source of energy that facilitates the breaking of the bromine-bromine bond, resulting in the formation of bromine radicals. These radicals are highly reactive and can then participate in the substitution reaction with alkanes, eventually leading to the formation of bromoalkanes.

Specifically, the energy from the UV light assists in breaking the Br-Br bond, allowing the bromine atoms to become radical species that can interact with the alkane molecules. This is essential for the reaction to occur, as alkanes are relatively unreactive due to their stable sigma bonds. By providing the necessary energy, UV light effectively enables the radical mechanism to proceed through various steps, including the initiation, propagation, and termination.

The other options describe aspects that do not accurately reflect the role of UV light in this reaction. Thus, emphasizing that UV light provides the energy necessary for the radical substitution aligns with the core principles of organic chemistry.