`(3c, 2e)` bond is present in

Options

A. `B_(2)H_(6)`
B. `BCl_(3)`
C. `Al_(2)Cl_(6)`
D. `NH_(3)`

Explanation

To determine which compound contains a (3c, 2e) bond, we can analyze the bonding in each of the given options step by step.

### Step 1: Understanding (3c, 2e) Bonds
A (3c, 2e) bond, also known as a three-centered two-electron bond, involves three atoms sharing two electrons. This type of bond is typically found in certain boron compounds, particularly in diborane.

### Step 2: Analyzing Each Option
1. **Ammonia (NH3)**:
- Structure: Nitrogen is sp³ hybridized with one lone pair and three bond pairs.
- Bonding: All bonds are (2c, 2e) bonds, where two electrons are shared between two atoms (N and H).
- Conclusion: **Not a (3c, 2e) bond.**

2. **Boron Trichloride (BCl3)**:
- Structure: Boron is sp² hybridized with a trigonal planar geometry.
- Bonding: All bonds are (2c, 2e) bonds between boron and chlorine atoms.
- Conclusion: **Not a (3c, 2e) bond.**

3. **Aluminum Chloride (Al2Cl6)**:
- Structure: This is a dimer of AlCl3. Each aluminum atom is bonded to three chlorine atoms.
- Bonding: The bonds formed are (2c, 2e) bonds, with no (3c, 2e) bonds present.
- Conclusion: **Not a (3c, 2e) bond.**

4. **Diborane (B2H6)**:
- Structure: Diborane has a unique structure with two terminal hydrogen atoms and two bridging hydrogen atoms.
- Bonding: The bridging hydrogens form (3c, 2e) bonds, where two electrons are shared among three centers (two boron atoms and one hydrogen atom).
- Conclusion: **This is a (3c, 2e) bond.**

### Final Answer
The compound that contains a (3c, 2e) bond is **Diborane (B2H6)**, which is option A.

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