Acetylene polymerizes in the presence of `Ni(CN)_2` under pressure to form mainly

Options

A.
B. `CH_2=CH-C-=CH`
C.
D. `CH_2=CH-C-=C-CH=CH_2`

Explanation

To solve the question regarding the polymerization of acetylene in the presence of `Ni(CN)2` under pressure, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Acetylene**: Acetylene (C2H2) is the simplest alkyne and has a triple bond between the two carbon atoms.

2. **Polymerization Process**: When acetylene is subjected to polymerization, especially in the presence of a catalyst like `Ni(CN)2` and under high pressure, it can undergo a reaction that leads to the formation of a polymer.

3. **Reaction Mechanism**: The polymerization involves the breaking of the triple bond in acetylene, allowing the carbon atoms to link together. The `Ni(CN)2` acts as a catalyst to facilitate this process.

4. **Formation of Cyclooctatetraene**: The polymerization of acetylene under these conditions leads to the formation of a cyclic compound. Specifically, it forms cyclooctatetraene (C8H8), which has alternating double bonds in a cyclic structure.

5. **Naming the Product**: The product formed is known as cyclooctatetraene, which can be represented as cyclo-1,3,5,7-octatetraene. This compound is characterized by its unique structure with alternating double bonds.

6. **Conclusion**: Therefore, the main product formed from the polymerization of acetylene in the presence of `Ni(CN)2` under pressure is cyclooctatetraene.

### Final Answer:
The main product formed is **cyclooctatetraene (C8H8)**.

---