Butane, C4H10\text{C}_4\text{H}_{10}C4H10, reacts with chlorine in the presence of ultraviolet radiation to form a mixture of chlorinated products. Which equation represents a propagation step in the mechanism for this reaction?
Cl2→⋅Cl+⋅Cl\text{Cl}_2 \rightarrow \cdot\text{Cl} + \cdot\text{Cl}Cl2→⋅Cl+⋅Cl
⋅Cl+⋅C4H8Cl→C4H8Cl2\cdot\text{Cl} + \cdot\text{C}_4\text{H}_8\text{Cl} \rightarrow \text{C}_4\text{H}_8\text{Cl}_2⋅Cl+⋅C4H8Cl→C4H8Cl2
⋅Cl+C4H9Cl→⋅C4H8Cl+HCl\cdot\text{Cl} + \text{C}_4\text{H}_9\text{Cl} \rightarrow \cdot\text{C}_4\text{H}_8\text{Cl} + \text{HCl}⋅Cl+C4H9Cl→⋅C4H8Cl+HCl
C4H9Cl+⋅Cl→C4H8Cl2+⋅H\text{C}_4\text{H}_9\text{Cl} + \cdot\text{Cl} \rightarrow \text{C}_4\text{H}_8\text{Cl}_2 + \cdot\text{H}C4H9Cl+⋅Cl→C4H8Cl2+⋅H
