Which of the following species can act both as an acid as well as a base ?

Options

A. `SO_(4)^(2-)`
B. `HSO_(4)^(-)`
C. `PO_(4)^(3-)`
D. `OH^(-)`

Explanation

To determine which species can act both as an acid and a base, we can analyze the options based on the Bronsted-Lowry acid-base theory. According to this theory, an acid is a substance that can donate a proton (H⁺), while a base is a substance that can accept a proton.

### Step-by-Step Solution:

1. **Understand the Definitions**:
- **Acid**: A species that donates a proton (H⁺).
- **Base**: A species that accepts a proton (H⁺).

2. **Analyze Each Species**:
- Let's denote the species as A, B, C, etc. (since the specific species are not provided in the question).

3. **Evaluate Species A**:
- If species A can only donate protons and cannot accept them, it is classified solely as an acid. Therefore, it cannot act as both an acid and a base.

4. **Evaluate Species B (HSO₄⁻)**:
- When HSO₄⁻ donates a proton, it forms SO₄²⁻, which is its conjugate base. This means HSO₄⁻ acts as an acid.
- When HSO₄⁻ accepts a proton, it forms H₂SO₄, which is its conjugate acid. This means HSO₄⁻ acts as a base.
- Since HSO₄⁻ can both donate and accept protons, it can act as both an acid and a base.

5. **Evaluate Species C**:
- If species C can only accept protons and cannot donate them, it is classified solely as a base. Therefore, it cannot act as both an acid and a base.

6. **Conclusion**:
- Based on the analysis, the only species that can act both as an acid and a base is **HSO₄⁻**.

### Final Answer:
The species that can act both as an acid and a base is **HSO₄⁻**.

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