When free Cl(g) atoms encounter O₃(g) molecules in the upper atmosphere, the following reaction mechanism is proposed to occur.
A) Cl(g) + O₃(g) ⇌ ClO(g) + O₂(g) (slow step)
B) ClO(g) + O₃(g) ⇌ Cl(g) + 2O₂(g) (fast step)
C) Cl(g) + O₃(g) ⇌ ClO(g) + O₂(g) (fast step)
D) ClO(g) + O₂(g) ⇌ Cl(g) + O₃(g) (slow step)