Conjugate acid of `HPO_4^-2` is

Options

A. `H_2PO_4^-1`
B. `H_3PO_4`
C. `PO_4^(3-)`
D. `HPO_3^(2-)`

Answer

To find the conjugate acid of \( HPO_4^{2-} \), we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Concept of Conjugate Acids and Bases**:
- A conjugate acid is formed when a base gains a hydrogen ion (\( H^+ \)).
- Conversely, a conjugate base is formed when an acid loses a hydrogen ion.

2. **Identify the Species**:
- We are given \( HPO_4^{2-} \). This species can act as a base because it can accept a hydrogen ion.

3. **Add a Hydrogen Ion**:
- To find the conjugate acid of \( HPO_4^{2-} \), we need to add a hydrogen ion (\( H^+ \)) to it:
\[ HPO_4^{2-} + H^+ \rightarrow H_2PO_4^{-} \]

4. **Result**:
- The resulting species after adding \( H^+ \) to \( HPO_4^{2-} \) is \( H_2PO_4^{-} \).
- Therefore, the conjugate acid of \( HPO_4^{2-} \) is \( H_2PO_4^{-} \).

### Final Answer:
The conjugate acid of \( HPO_4^{2-} \) is \( H_2PO_4^{-} \).

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