Choose the chain terminating step (1) \[{{H}_{2}}\to {{H}^{\bullet }}+{{H}^{\bullet }}\] (2) \[B{{r}_{2}}\to B{{r}^{\bullet }}+B{{r}^{\bullet }}\] (3) \[B{{r}^{\bullet }}+HBr\to {{H}^{\bullet }}+B{{r}_{2}}\] (4) \[{{H}^{\bullet }}+B{{r}_{2}}\to HBr+B{{r}^{\bullet }}\] (5) \[B{{r}^{\bullet }}+B{{r}^{\bullet }}\to B{{r}_{2}}\] [RPET 2000]

• A. 1
• B. 3
• C. 4
• D. 5