Which of the following molecular hydrises acts as a Lewis acid?

Options

A. `NH_(3)`
B. `H_(2)O`
C. `B_(2)H_(6)`
D. `CH_(4)`

Answer

To determine which of the following molecular hydrides acts as a Lewis acid, we need to understand the definition of a Lewis acid. A Lewis acid is a substance that can accept an electron pair to form a dative bond, which means it must have an empty orbital available for this purpose.

### Step-by-Step Solution:

1. **Identify the Definition of Lewis Acid**:
- A Lewis acid is defined as a substance that can accept an electron pair. This requires the presence of an empty orbital.

2. **Analyze the Given Hydrides**:
- We will analyze the molecular hydrides provided in the question, which include NiH3, H2O, CH4, and B2H6.

3. **Examine NiH3 (Nickel Hydride)**:
- NiH3 has a central nickel atom, which has d-orbitals available. However, it primarily has lone pairs and does not typically act as a Lewis acid.

4. **Examine H2O (Water)**:
- Water has lone pairs on the oxygen atom, allowing it to act as a Lewis base (donating electron pairs) rather than a Lewis acid.

5. **Examine CH4 (Methane)**:
- Methane is an electron-precise compound with no lone pairs or empty orbitals. Therefore, it cannot act as a Lewis acid.

6. **Examine B2H6 (Diborane)**:
- The monomer of B2H6 is BH3 (Boron Trihydride). Boron has an electronic configuration of 2s² 2p¹, which means it has an empty p orbital. This allows boron to accept an electron pair, making B2H6 a Lewis acid.

7. **Conclusion**:
- Among the given options, B2H6 acts as a Lewis acid due to the presence of an empty orbital on boron, which allows it to accept electron pairs.

### Final Answer:
**B2H6 acts as a Lewis acid.**

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