Which of these reactions proceeds by a free radical mechanism in the presence of UV light?

In order to determine which reactions proceed by a free radical mechanism in the presence of UV light, we need to consider a few key characteristics of free radical reactions:

1. Initiation: Free radicals are generated, often through the homolytic cleavage of a bond due to UV light.
2. Propagation: Free radicals react with other substances, leading to new radicals and continuing the reaction.
3. Termination: Reactions may end when two radicals combine to form a stable molecule.

Common examples of reactions that can proceed via a free radical mechanism in UV light include:

• The halogenation of alkanes (e.g., chlorination or bromination of methane).
• Polymerization reactions (e.g., formation of polyethylene from ethylene).

To identify specific reactions, please provide a list of reactions or options that you are considering for analysis.