The following is a primary phosphate ion 

Options

A. `H_(2)PO_(4)^(2-)`
B. `H_(2)PO_(3)^(-)`
C. `H_(2)PO_(4)^(-)`
D. `PO_(4)^(3-)`

Answer

To determine which of the given ions is a primary phosphate ion, we need to analyze the options based on the definitions of primary, secondary, and tertiary phosphate ions.

### Step-by-Step Solution:

1. **Understanding Phosphoric Acid**:
- The formula for phosphoric acid is H₃PO₄. It contains three hydrogen ions that can be lost sequentially.

2. **Identifying the Ions**:
- The options provided are:
- H₂PO₄²⁻
- H₂PO₃⁻
- H₃PO₄
- PO₄³⁻

3. **Losing Hydrogen Ions**:
- When phosphoric acid (H₃PO₄) loses one hydrogen ion (H⁺), it forms H₂PO₄⁻. This ion is known as the **primary phosphate ion**.
- If H₂PO₄⁻ loses another hydrogen ion, it forms HPO₄²⁻, which is known as the **secondary phosphate ion**.
- If HPO₄²⁻ loses another hydrogen ion, it forms PO₄³⁻, which is known as the **tertiary phosphate ion**.

4. **Analyzing the Options**:
- H₂PO₄⁻: This is the primary phosphate ion (formed from H₃PO₄).
- H₂PO₃⁻: This is not a phosphate ion derived from phosphoric acid; it is a different species.
- H₃PO₄: This is phosphoric acid itself, not a phosphate ion.
- PO₄³⁻: This is the tertiary phosphate ion (formed from HPO₄²⁻).

5. **Conclusion**:
- The only primary phosphate ion from the options is **H₂PO₄⁻**.

### Final Answer:
The primary phosphate ion is **H₂PO₄⁻**.