No X-X bond exists in which of the following compounds having general form of `X_2H_6` ?

Options

A. `B_2H_6`
B. `C_2H_6`
C. `Al_2H_6`
D. `Si_2H_6`

Answer

To solve the question of which compound with the general formula \( X_2H_6 \) does not have an \( X-X \) bond, we will analyze the bonding in the given compounds: \( B_2H_6 \), \( C_2H_6 \), \( Al_2H_6 \), and \( Si_2H_6 \).

### Step-by-Step Solution:

1. **Identify the Compounds**: The compounds we need to analyze are:
- \( B_2H_6 \) (Diborane)
- \( C_2H_6 \) (Ethane)
- \( Al_2H_6 \) (Dihydride of Aluminum)
- \( Si_2H_6 \) (Silane)

2. **Analyze \( B_2H_6 \)**:
- In diborane, each boron atom has three valence electrons. The structure consists of two boron atoms bonded to six hydrogen atoms.
- The bonding involves three-center two-electron bonds where hydrogen atoms bridge between boron atoms.
- There are no direct \( B-B \) bonds; hence, \( B_2H_6 \) does not have a \( B-B \) bond.

3. **Analyze \( C_2H_6 \)**:
- In ethane, each carbon atom has four valence electrons. Each carbon atom forms single bonds with three hydrogen atoms and shares one electron with the other carbon atom.
- This results in a \( C-C \) bond, meaning \( C_2H_6 \) does have a \( C-C \) bond.

4. **Analyze \( Al_2H_6 \)**:
- In aluminum hydride, each aluminum atom has three valence electrons. Similar to diborane, aluminum atoms bond with hydrogen atoms.
- The bonding involves three-center two-electron bonds, and there are no direct \( Al-Al \) bonds. Thus, \( Al_2H_6 \) does not have an \( Al-Al \) bond.

5. **Analyze \( Si_2H_6 \)**:
- In silane, each silicon atom has four valence electrons. Each silicon atom forms single bonds with three hydrogen atoms and shares one electron with the other silicon atom.
- This results in a \( Si-Si \) bond, meaning \( Si_2H_6 \) does have a \( Si-Si \) bond.

6. **Conclusion**:
- From the analysis, we find that \( B_2H_6 \) and \( Al_2H_6 \) do not have \( X-X \) bonds, while \( C_2H_6 \) and \( Si_2H_6 \) do. However, since the question asks for a compound with no \( X-X \) bond, the answer is \( B_2H_6 \).

### Final Answer:
**No \( X-X \) bond exists in \( B_2H_6 \) (Diborane).**