Which of the following can act both as a Bronsted acid and a Bronsted base?

Options

A. (a) `O_(2)^(Theta)`
B. (b) `HCl`
C. (c) `HSO_(4)^(Theta)`
D. (d) `Na_(2)CO_(3)`

Explanation

To determine which of the given substances can act both as a Bronsted acid and a Bronsted base, we need to understand the definitions of Bronsted acids and bases:

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

Now, let's analyze the options provided:

### Step 1: Identify the substances
Assuming the options are:
- A) HCl
- B) HSO4⁻
- C) H2O
- D) NH3

### Step 2: Analyze each substance
- **HCl**:
- As a Bronsted acid: HCl can donate H⁺ to form Cl⁻.
- As a Bronsted base: HCl cannot accept H⁺ ions.
- Conclusion: HCl can only act as a Bronsted acid.

- **HSO4⁻**:
- As a Bronsted acid: HSO4⁻ can donate H⁺ to form SO4²⁻.
- As a Bronsted base: HSO4⁻ can accept H⁺ to form H2SO4.
- Conclusion: HSO4⁻ can act as both a Bronsted acid and a Bronsted base.

- **H2O**:
- As a Bronsted acid: H2O can donate H⁺ to form OH⁻.
- As a Bronsted base: H2O can accept H⁺ to form H3O⁺.
- Conclusion: H2O can act as both a Bronsted acid and a Bronsted base.

- **NH3**:
- As a Bronsted acid: NH3 cannot donate H⁺ ions.
- As a Bronsted base: NH3 can accept H⁺ to form NH4⁺.
- Conclusion: NH3 can only act as a Bronsted base.

### Step 3: Conclusion
From the analysis, we find that both HSO4⁻ and H2O can act as both Bronsted acids and Bronsted bases. However, if we are to choose one based on the options provided, HSO4⁻ is the most commonly recognized example of a substance that can act as both.

### Final Answer
The correct answer is **HSO4⁻**.