Which of the following can act as Lowry-Bronsted acid as well as base?

Options

A. HCI
B. `SO_(4)^(2-)`
C. `HPO_(4)^(2-)`
D. `Br^(-)`

Answer

To determine which of the following substances can act as both a Lewis acid and a Lewis base according to the Brønsted-Lowry theory, we need to understand the definitions of Brønsted-Lowry acids and bases:

1. **Brønsted-Lowry Acid**: A substance that donates a proton (H⁺).
2. **Brønsted-Lowry Base**: A substance that accepts a proton (H⁺).

Now, let's analyze the given substance, HPO₄²⁻ (dihydrogen phosphate ion):

### Step 1: Identify the structure of HPO₄²⁻
- The HPO₄²⁻ ion has a central phosphorus atom surrounded by four oxygen atoms, one of which is bonded to a hydrogen atom (OH group).

### Step 2: Determine if it can act as a Brønsted-Lowry Acid
- The hydrogen atom in the OH group can be donated as a proton (H⁺). Therefore, HPO₄²⁻ can act as a Brønsted-Lowry acid.

### Step 3: Determine if it can act as a Brønsted-Lowry Base
- The two negatively charged oxygen atoms can accept protons (H⁺). This means that HPO₄²⁻ can also act as a Brønsted-Lowry base.

### Conclusion
Since HPO₄²⁻ can both donate a proton (acting as an acid) and accept a proton (acting as a base), it qualifies as a substance that can act as both a Brønsted-Lowry acid and base.

Thus, the correct answer is HPO₄²⁻.

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