The chemical reactions provided describe the involvement of chlorine monoxide (ClO) and bromine monoxide (BrO) in catalytic cycles that deplete ozone (O₃). These reactions are associated with substances that contain chlorine and bromine, which are known to catalyze the breakdown of ozone in the stratosphere.
1. The first reaction shows ClO and BrO reacting to form Cl, Br, and O₂.
2. The second and third reactions show Cl and Br reacting with ozone to reform ClO and BrO while producing O₂.
These chemical reactions are characteristic of the way certain substances deplete ozone. The substances that typically contain chlorine (Cl) and bromine (Br) and are known to be involved in ozone depletion include chlorofluorocarbons (CFCs) and halons.
Given the context, the correct answer to the question is:
a. chlorofluorocarbons
