Which of the following species is an acid and also a conjugate base of another acid

Options

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

Explanation

To solve the question "Which of the following species is an acid and also a conjugate base of another acid?", we need to analyze each option provided and determine if any species can act both as an acid and as a conjugate base.

### Step-by-Step Solution:

1. **Understand the Definitions**:
- An **acid** is a species that can donate a proton (H⁺).
- A **conjugate base** is what remains after an acid donates a proton; it can accept a proton.

2. **Analyze Each Option**:
- **Option 1: HSO₄⁻ (Hydrogen sulfate ion)**:
- HSO₄⁻ can donate a proton to become SO₄²⁻ (sulfate ion), thus acting as an acid.
- It can also accept a proton to become H₂SO₄ (sulfuric acid), thus acting as a conjugate base.
- Therefore, HSO₄⁻ is both an acid and a conjugate base.

- **Option 2: H₂SO₄ (Sulfuric acid)**:
- H₂SO₄ can donate a proton to become HSO₄⁻, acting as an acid.
- However, it cannot accept a proton to become another species, so it cannot act as a conjugate base.
- Thus, H₂SO₄ is not the answer.

- **Option 3: OH⁻ (Hydroxide ion)**:
- OH⁻ can accept a proton to form H₂O, acting as a conjugate base.
- It cannot donate a proton, so it cannot act as an acid.
- Therefore, OH⁻ is not the answer.

- **Option 4: H₃O⁺ (Hydronium ion)**:
- H₃O⁺ can donate a proton to become H₂O, acting as an acid.
- However, it cannot accept another proton, so it cannot act as a conjugate base.
- Thus, H₃O⁺ is not the answer.

3. **Conclusion**:
- The only species that can act both as an acid and as a conjugate base is **HSO₄⁻**.
- Therefore, the answer to the question is **Option 1: HSO₄⁻**.