A Level Chemistry OCR Practice Exam

In a chain reaction during radical substitution, propagation steps are crucial to the process. Propagation involves a series of reactions where the radicals generated continue to react and form new radicals. Each of these steps leads to the formation of additional reactive species, allowing the reaction to proceed rapidly and produce multiple products.

The nature of this chain reaction means that existing radicals can react with stable molecules to produce more radicals, which can further propagate the reaction. This interconnected series of reactions underscores how radical substitution can lead to a complex mixture of products rather than a single product, illustrating the dynamic and branching nature of the process.

The other options do not accurately reflect the behavior of a chain reaction in this context. Electrons do not simply get lost from the system; rather, the focus is on the rearrangement of electrons to form radicals. A constant rate of product formation is not characteristic of the unpredictable and variable nature of product diversity in radical substitutions. Additionally, temperature can change as the reaction progresses due to the exothermic nature of many of these reactions, which means it is not likely to remain constant throughout the process.