In which of the following , delocalisation of `pi-`electrons is/are possible?

Options

A. `CH_(2)=CH_(2)`
B. `CH_(3)-CH_(2)-CH=CH_(2)`
C. `CH_(2)=CH-CH=CH_(2)`
D. `CH_(2)=CH-CH_(2)-CH=CH_(2)`

Answer

To determine in which of the given compounds delocalization of π-electrons is possible, we need to identify if there is a conjugated system present. A conjugated system is characterized by alternating single and double bonds, which allows for the overlap of π-orbitals and the delocalization of π-electrons across the molecule.

### Step-by-Step Solution:

1. **Identify the Compounds**:
We need to analyze the given compounds to check for the presence of alternating single and double bonds.

2. **Analyze Each Compound**:
- **Compound 1**: Only has double bonds (e.g., C=C).
- **Conclusion**: No conjugation; no delocalization of π-electrons is possible.

- **Compound 2**: Contains a single bond followed by a double bond (e.g., C-C=C).
- **Conclusion**: No conjugation; no delocalization of π-electrons is possible.

- **Compound 3**: Has a structure like CH2=CH-CH=CH2.
- **Conclusion**: This compound shows alternating double and single bonds (conjugation). Therefore, π-electrons can delocalize across the molecule.

- **Compound 4**: Has a double bond followed by two single bonds and then another double bond (e.g., C=C-C-C=).
- **Conclusion**: There is no alternating pattern of single and double bonds; thus, no delocalization of π-electrons is possible.

3. **Final Conclusion**:
The only compound that allows for the delocalization of π-electrons is Compound 3 (CH2=CH-CH=CH2).

### Answer:
The delocalization of π-electrons is possible in **Compound 3**.