What is the required condition for the chlorination of methane?

• A. Ultraviolet light (UV)
• B. Heat at high temperature
• C. A metal catalyst
• D. High pressure

Answer: (A)

Ultraviolet light provides the energy to break the chlorine–chlorine bond and start a free-radical chain reaction. When Cl2 absorbs UV light, it splits into two chlorine radicals. These highly reactive Cl• species remove a hydrogen from methane, forming HCl and a methyl radical (CH3•). The methyl radical then reacts with another Cl2 molecule to form chloromethane and regenerates a Cl•, allowing the process to continue in a chain reaction. This radical mechanism explains why light is essential for chlorinating methane under typical conditions. Heat alone can drive reactions but is not the defining condition here, and a metal catalyst or high pressure isn’t required for this process.