What type of radiation is responsible for breaking the Cl-Cl bond during initiation?

The type of radiation responsible for breaking the Cl-Cl bond during the initiation phase of a reaction, such as in a free radical chain reaction, is ultraviolet radiation.

When UV radiation is absorbed by chlorine molecules (Cl2), it provides enough energy to break the covalent bond between the two chlorine atoms. This process results in the formation of two chlorine radicals. The energy of the UV radiation matches the bond dissociation energy of the Cl-Cl bond, making it suitable for bond breaking.

In contrast, other types of radiation listed do not have the right energy levels to effectively dissociate the Cl-Cl bond. For instance, X-ray and gamma radiation possess much higher energy, which is typically more suited for disrupting atomic nuclei or causing ionization rather than breaking covalent bonds in molecular compounds. Conversely, infrared radiation has lower energy, primarily involved in vibrating molecular bonds rather than breaking them. Therefore, ultraviolet radiation is the correct choice due to its ability to effectively break the chlorine-chlorine bond during initiation.