Choose the chain terminating step
(1) `H_(2) rarr H^(*)+H^(*)`
(2) `Br_(2) rarr Br^(*) + Br^(*)`
(3) `Br^(*) + HBr rarr H^(*) + Br_(2)`
(4) `H^(*) + Br_(2) rarr HBr + Br^(*)`
(5) `Br^(*) + Br^(*) rarr Br_(2)`

Options

A. 1
B. 3
C. 4
D. 5

Answer

To determine the chain terminating step from the given options, we need to identify which reaction leads to the formation of stable products without any free radicals remaining.

### Step-by-Step Solution:

1. **Understanding Chain Termination**:
- A chain terminating step occurs when free radicals combine to form a stable product, effectively stopping the chain reaction. In these steps, the free radicals are consumed and do not appear in the products.

2. **Analyzing Each Option**:
- **Option 1**: `H2 → H* + H*`
- This reaction generates two hydrogen radicals (H*), which means it does not terminate the chain.
- **Option 2**: `Br2 → Br* + Br*`
- Similar to option 1, this generates two bromine radicals (Br*), so it does not terminate the chain.
- **Option 3**: `Br* + HBr → H* + Br2`
- In this reaction, a bromine radical reacts with HBr to produce another radical (H*) and Br2. This does not terminate the chain as radicals are still present.
- **Option 4**: `H* + Br2 → HBr + Br*`
- Here, a hydrogen radical reacts with Br2, producing HBr and leaving a bromine radical (Br*). This also does not terminate the chain.
- **Option 5**: `Br* + Br* → Br2`
- In this reaction, two bromine radicals combine to form Br2, a stable molecule. No radicals are left in the products, indicating that this step terminates the chain.

3. **Conclusion**:
- The chain terminating step is **Option 5**: `Br* + Br* → Br2`.

### Final Answer:
The chain terminating step is **Option 5**: `Br* + Br* → Br2`.