Which of the followinG compounds has a 3-centre two electron bond ?

Options

A. Diborane
B. `CO_(2)`
C. Boron trifluoride
D. Ammonia

Explanation

To determine which of the given compounds has a 3-center 2-electron bond, we need to understand what a 3-center 2-electron bond is. This type of bond involves three atoms sharing a total of only two electrons, which typically occurs in electron-deficient compounds.

### Step-by-Step Solution:

1. **Understanding 3-Center 2-Electron Bond**:
- A 3-center 2-electron bond is formed when three atoms share two electrons. This bond is often found in compounds that are electron-deficient.

2. **Analyzing the Compounds**:
- We need to analyze the given compounds one by one to see if they exhibit a 3-center 2-electron bond.

3. **Compound 1: Carbon Dioxide (CO₂)**:
- In CO₂, carbon is bonded to two oxygen atoms through double bonds. Each double bond involves the sharing of four electrons (two from carbon and two from oxygen). Therefore, CO₂ does not have a 3-center 2-electron bond.

4. **Compound 2: Ammonia (NH₃)**:
- In ammonia, nitrogen is bonded to three hydrogen atoms. Each N-H bond involves the sharing of two electrons (one from nitrogen and one from hydrogen). Thus, ammonia does not exhibit a 3-center 2-electron bond.

5. **Compound 3: Boron Trifluoride (BF₃)**:
- In BF₃, boron is bonded to three fluorine atoms. Each bond involves the sharing of two electrons. However, BF₃ does not have a 3-center 2-electron bond since all electrons are shared between two atoms (boron and each fluorine) rather than three atoms.

6. **Compound 4: Diborane (B₂H₆)**:
- Diborane has a unique structure where two boron atoms are connected by two hydrogen atoms in a bridging manner. Each boron atom forms four bonds, but since boron is electron-deficient (having only three valence electrons), the two hydrogen atoms act as bridges between the two boron atoms. This results in a 3-center 2-electron bond, where the two electrons from the bridging hydrogen are shared between the two boron atoms and the hydrogen atom itself.

7. **Conclusion**:
- Among the given compounds, **diborane (B₂H₆)** is the only compound that exhibits a 3-center 2-electron bond.

### Final Answer:
**Diborane (B₂H₆)** has a 3-center 2-electron bond.