The species which can act both as Bronsted acid and base is

Options

A. `CO_3^2-`
B. `NO_3^-`
C. `HSO_4^-`
D. `SO_4^2-`

Answer

To determine which species can act both as a Brønsted acid and a Brønsted base, we need to understand the definitions of these terms:

1. **Brønsted Acid**: A substance that can donate a proton (H⁺ ion).
2. **Brønsted Base**: A substance that can accept a proton (H⁺ ion).

Now, let's analyze the species HSO₄⁻ (hydrogen sulfate ion):

### Step 1: Identify if HSO₄⁻ can act as a Brønsted Acid
- HSO₄⁻ can donate a proton (H⁺) to become SO₄²⁻ (sulfate ion).

**Reaction**:
\[ \text{HSO}_4^- \rightarrow \text{SO}_4^{2-} + \text{H}^+ \]

### Step 2: Identify if HSO₄⁻ can act as a Brønsted Base
- HSO₄⁻ can accept a proton (H⁺) to become H₂SO₄ (sulfuric acid).

**Reaction**:
\[ \text{HSO}_4^- + \text{H}^+ \rightarrow \text{H}_2\text{SO}_4 \]

### Conclusion
Since HSO₄⁻ can both donate a proton (acting as a Brønsted acid) and accept a proton (acting as a Brønsted base), it qualifies as a species that can act as both.

Thus, the answer is:
**HSO₄⁻ is the species that can act both as a Brønsted acid and a Brønsted base.**

---