The C-Cl bond length is shortest in :

Options

A. `CH_(2)=CH-underset(* *)overset(* *)Cl:`
B. `CH_(3)-Cl`
C. `C_(6)H_(5)-CH_(2)-Cl`
D. `CH_(2)=CH-CH_(2)-Cl`

Explanation

To determine which C-Cl bond length is shortest among the given options, we need to analyze the resonance and hybridization effects in each compound.

### Step-by-Step Solution:

1. **Identify the Compounds**:
Let's consider the compounds mentioned in the question. We will analyze the bond lengths in each of the compounds provided in the options.

2. **Analyze Resonance**:
- **Option A: CH2=CH-CH2Cl** (Allyl chloride)
- In this compound, the C-Cl bond is adjacent to a double bond (C=C). This allows for resonance stabilization, where the lone pair on the chlorine can participate in resonance with the double bond, leading to a partial double bond character in the C-Cl bond.

- **Option B: CH3-CH2-CH2Cl** (1-chloropropane)
- This compound has a single C-Cl bond with no adjacent double bonds or resonance structures. The C-Cl bond is a typical single bond and will be longer than a bond with partial double bond character.

- **Option C: CH2=CH-CH2Cl** (same as option A)
- This is the same as option A and will have the same resonance effect, thus having a shorter C-Cl bond length due to resonance.

- **Option D: CH3-CH=CHCl** (3-chloropropene)
- In this compound, the C-Cl bond is also adjacent to a double bond, allowing for some resonance. However, the resonance effect may not be as strong as in option A due to the positioning of the double bond.

3. **Compare the C-Cl Bond Lengths**:
- The presence of resonance in option A (CH2=CH-CH2Cl) gives the C-Cl bond a partial double bond character, making it shorter than the C-Cl bond in option B (1-chloropropane) which has no resonance.
- Option C is the same as option A, so it will also have a short C-Cl bond.
- Option D has some resonance but not as effectively as option A.

4. **Conclusion**:
The C-Cl bond length is shortest in **option A (CH2=CH-CH2Cl)** due to the resonance effect that gives the bond partial double bond character.

### Final Answer:
The C-Cl bond length is shortest in **option A (CH2=CH-CH2Cl)**.

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