In which of the following pairs, indicated bond is of greater strength :
`CH_(3) - CH_(2) underset(uarr" ")-Br " and " CH_(3) - CH_(2)underset(uarr" ")-Cl`

Answer

To determine which bond is stronger between `CH3-CH2-Br` and `CH3-CH2-Cl`, we need to analyze the bond strength based on the atomic properties of chlorine (Cl) and bromine (Br).

### Step-by-Step Solution:

1. **Identify the Bonds**:
- We have two bonds to compare:
- `C-Br` in `CH3-CH2-Br`
- `C-Cl` in `CH3-CH2-Cl`

2. **Consider Atomic Size**:
- Chlorine (Cl) is smaller in size compared to Bromine (Br).
- As we move down the group in the periodic table, the size of the atoms increases. Therefore, Br is larger than Cl.

3. **Evaluate Overlapping**:
- The strength of a bond is influenced by the extent of orbital overlap between the atoms involved.
- In `C-Cl`, the overlap occurs between the 2p orbital of carbon and the 3p orbital of chlorine.
- In `C-Br`, the overlap occurs between the 2p orbital of carbon and the 4p orbital of bromine.

4. **Analyze the Overlapping**:
- The greater the overlap, the stronger the bond.
- Since chlorine is smaller, the overlap between carbon's 2p and chlorine's 3p orbitals is better than the overlap between carbon's 2p and bromine's 4p orbitals.

5. **Conclusion**:
- Because of the better overlap in `C-Cl` compared to `C-Br`, the bond `C-Cl` is stronger than `C-Br`.
- Thus, the bond in `CH3-CH2-Cl` is of greater strength than the bond in `CH3-CH2-Br`.

### Final Answer:
The bond `C-Cl` in `CH3-CH2-Cl` is of greater strength than the bond `C-Br` in `CH3-CH2-Br`.

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