The compound having longest `C-Cl` bond is

Options

A.
B.
C.
D.

Explanation

To determine which compound has the longest C-Cl bond, we need to analyze the effect of resonance and bond order in the given compounds. Here’s a step-by-step breakdown of the solution:

### Step 1: Understand Bond Length and Bond Order
- The bond length is inversely proportional to the bond order. This means that as the bond order increases, the bond length decreases. Conversely, a lower bond order results in a longer bond length.

### Step 2: Identify the Compounds
- We need to analyze the given compounds (not specified in the question but typically would include chlorobenzene, alkyl chlorides, etc.) to see which has resonance and how it affects the C-Cl bond.

### Step 3: Analyze Resonance Effects
- **Chlorobenzene**: In chlorobenzene, the chlorine atom can participate in resonance with the benzene ring. This resonance leads to a partial double bond character in the C-Cl bond, increasing the bond order and thus decreasing the bond length.

- **Alkyl Chlorides**: In simple alkyl chlorides (like chloroethane), there is no resonance effect. The C-Cl bond retains its single bond character, resulting in a higher bond length compared to chlorobenzene.

### Step 4: Compare the Compounds
- **Chlorobenzene**: Has resonance, leading to a shorter C-Cl bond.
- **Alkyl Chlorides**: Lack resonance, resulting in a longer C-Cl bond compared to chlorobenzene.

### Step 5: Identify the Compound with the Longest C-Cl Bond
- Since alkyl chlorides do not have resonance and thus have a lower bond order compared to chlorobenzene, they will have the longest C-Cl bond. Among the alkyl chlorides, the one with the least steric hindrance or branching will have the longest bond.

### Conclusion
- The compound with the longest C-Cl bond is likely to be an alkyl chloride (e.g., chloroethane) due to the absence of resonance.