Acid base theories are important to understand the role of many substances in different reactions. Different theories are in practice which have advantages as well as limitations at their level. We always consider most convenient theory under the given conditions.
Which of the following is not Bronsted base

Options

A. `HS^(-)`
B. `CH_(3)COOH`
C. HF
D. `H_(3)O^(+)`

Answer

To determine which of the given substances is not a Brønsted base, we need to understand the definition of a Brønsted base. A Brønsted base is defined as a substance that can accept a proton (H⁺ ion).

### Step-by-Step Solution:

1. **Understand the Definition of Brønsted Base**:
- A Brønsted base is a substance that can accept protons (H⁺ ions).

2. **Analyze the Given Options**:
- Let's consider the possible options: Acetic acid (CH₃COOH), HF (hydrofluoric acid), H₃O⁺ (hydronium ion), and HS⁻ (hydrosulfide ion).

3. **Evaluate Each Option**:
- **Acetic Acid (CH₃COOH)**: This is a weak acid and can donate a proton but cannot accept one. Therefore, it is not a Brønsted base.
- **HF (Hydrofluoric Acid)**: This is also an acid that donates protons and does not accept them. Hence, it is not a Brønsted base.
- **H₃O⁺ (Hydronium Ion)**: This ion has already accepted a proton and is positively charged. It cannot accept another proton, so it is not a Brønsted base.
- **HS⁻ (Hydrosulfide Ion)**: This ion can accept a proton to form H₂S (hydrogen sulfide), making it a Brønsted base.

4. **Conclusion**:
- The substances that are not Brønsted bases from the given options are Acetic Acid (CH₃COOH), HF, and H₃O⁺. Therefore, any of these options can be considered correct, depending on the specific context of the question.

### Final Answer:
The substances that are not Brønsted bases are Acetic Acid (CH₃COOH), HF, and H₃O⁺.