Consider this step in a radical reaction: $\mathrm{Cl}\cdot$ + ${\mathrm{CH}}_4$ → ${\mathrm{CH}}_3\cdot$ + ${\mathrm{HCl}}_{\mathrm{}}$. What type of step is this in the radical chain mechanism?

• A. Propagation
• B. Initiation
• C. Termination
• D. Rearrangement

Answer: (A)

Verified step by step guidance

1. Identify the species involved in the reaction step: a chlorine radical (Cl·) reacts with methane (CH₄) to form a methyl radical (CH₃·) and hydrogen chloride (HCl).
2. Recall the three main types of steps in a radical chain mechanism: initiation, propagation, and termination.
3. Understand that initiation steps generate radicals from non-radical species, usually by homolytic bond cleavage (e.g., Cl₂ → 2 Cl·).
4. Recognize that propagation steps involve radicals reacting with stable molecules to form new radicals, thus sustaining the chain reaction.
5. Note that termination steps involve two radicals combining to form a stable molecule, ending the chain reaction. Since this step forms a new radical and consumes a radical, it fits the propagation step.