Which of the following can act as a lewis acid ?

Options

A. `H_2O`
B. `B(OH)_3`
C. `BF_3`
D. Both (2) & (3)

Answer

To determine which of the given species can act as a Lewis acid, we need to understand the definition of a Lewis acid. According to Lewis theory, a Lewis acid is a species that can accept a lone pair of electrons. This typically requires the species to have a vacant or unoccupied orbital.

Let's analyze the given options step by step:

### Step 1: Analyze Water (H2O)
- **Configuration**: H2O has oxygen as the central atom. The electronic configuration of oxygen is 1s² 2s² 2p⁴.
- **Lone Pairs**: In H2O, oxygen has two lone pairs of electrons.
- **Vacant Orbitals**: Oxygen does not have a vacant orbital available to accept electrons. Therefore, H2O cannot act as a Lewis acid.

**Conclusion**: H2O is NOT a Lewis acid.

### Step 2: Analyze Oxygen (O2)
- **Configuration**: The electronic configuration of oxygen is the same as mentioned above (1s² 2s² 2p⁴).
- **Lone Pairs**: In O2, each oxygen atom has two lone pairs.
- **Vacant Orbitals**: Similar to H2O, elemental oxygen does not have vacant orbitals to accept electrons. Thus, O2 cannot act as a Lewis acid.

**Conclusion**: O2 is NOT a Lewis acid.

### Step 3: Analyze Boron Hydroxide (B(OH)3)
- **Configuration**: Boron has an electronic configuration of 1s² 2s² 2p¹.
- **Lone Pairs**: In B(OH)3, boron is bonded to three hydroxyl groups (OH). Boron has only three valence electrons and can form three bonds.
- **Vacant Orbitals**: After forming these bonds, boron has an empty p orbital available to accept a lone pair of electrons. Therefore, B(OH)3 can act as a Lewis acid.

**Conclusion**: B(OH)3 IS a Lewis acid.

### Step 4: Analyze Boron Trifluoride (BF3)
- **Configuration**: The electronic configuration of boron is the same as mentioned above (1s² 2s² 2p¹).
- **Lone Pairs**: In BF3, boron is bonded to three fluorine atoms.
- **Vacant Orbitals**: After forming these bonds, boron has an empty p orbital available to accept a lone pair of electrons. Therefore, BF3 can also act as a Lewis acid.

**Conclusion**: BF3 IS a Lewis acid.

### Final Answer:
The species that can act as Lewis acids from the given options are **B(OH)3 and BF3**.

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