Explain why ultraviolet light is needed for radical formation.

The cause for the need for ultraviolet (UV) light in radical formation during the chlorination of alkanes is the energy required to break the Cl-Cl bond. This energy is provided by UV light, which initiates the process by promoting the dissociation of chlorine molecules into chlorine radicals. The mechanism involves the absorption of UV light, leading to the homolytic cleavage of the Cl-Cl bond, resulting in two reactive chlorine radicals. The effect of this radical formation is the initiation of a chain reaction that allows for the substitution of hydrogen atoms in alkanes. Consequently, this process enables the chlorination of alkanes, producing chlorinated hydrocarbons.