Classifying reaction steps in free-radical substitution Steps: - Define key stages: Initiation generates radicals from stable molecules; propagation involves radicals forming products while regenerating radicals; termination combines radicals into stable molecules. - Examine Step 1: Cl• radical reacts with CH₄ to yield CH₃• radical and HCl product, consuming one radical but producing another to continue the chain. - Examine Step 2: CH₃• radical reacts with Cl₂ to yield CH₃Cl product and Cl• radical, again sustaining the radical cycle. - Identify both as propagation since they propagate the chain reaction without net radical gain or loss. Why D is correct: - Propagation steps regenerate radicals to sustain the chain, as seen in both reactions where one radical input equals one radical output per definition. Why the others are wrong: - A: Step 1 requires an existing Cl• radical, so it cannot be initiation, which starts with no radicals. - B: Step 2 produces a Cl• radical, so it is not termination, which eliminates radicals. - C: Step 1 generates a new radical type but needs an initial radical, ruling out initiation; …