Which of the following can not act as a bronsted base?

Options

A. `NH_(3)`
B. `BF_(3)`
C. `H_(3)O^(+)`
D. `H_(2)O`

Answer

To determine which of the given options cannot act as a Brønsted base, we first need to understand what a Brønsted base is. A Brønsted base is defined as a substance that can accept protons (H⁺ ions).

Let's analyze the options one by one:

1. **NH₃ (Ammonia)**:
- Ammonia can accept a proton to form NH₄⁺ (ammonium ion).
- Therefore, NH₃ can act as a Brønsted base.

2. **BF₃ (Boron Trifluoride)**:
- BF₃ does not have a proton to accept; instead, it has an empty p-orbital and can accept electron pairs, making it a Lewis acid rather than a Brønsted base.
- Therefore, BF₃ cannot act as a Brønsted base.

3. **H₃O⁺ (Hydronium Ion)**:
- The hydronium ion can donate a proton to form water (H₂O), which means it acts as a Brønsted acid.
- Therefore, H₃O⁺ cannot act as a Brønsted base.

4. **H₂O (Water)**:
- Water can accept a proton to form H₃O⁺, which means it can act as a Brønsted base.
- Therefore, H₂O can act as a Brønsted base.

From the analysis above, the substances that cannot act as Brønsted bases are BF₃ and H₃O⁺.

Thus, the correct answer to the question "Which of the following cannot act as a Brønsted base?" is **BF₃** and **H₃O⁺**.