Which of the following are conjugate acid-base pairs ?

Options

A. `HCO_(3)^(-)CO_(3)^(2-)`
B. `C_(6)H_(5)overset(+)NH_(3),C_(6)H_(5)NH_(2)`
C. `H_(2)PO_(2)^(-),H_(2)PO_(3)^(-),HC_(2)O_(4)^(-)`
D. `OH^(-),H^(+)`

Answer

To determine which of the following are conjugate acid-base pairs, we need to understand the concept of conjugate acids and bases. A conjugate acid is formed when a base gains a proton (H⁺), while a conjugate base is formed when an acid loses a proton.

### Step-by-Step Solution:

1. **Identify the Compounds**: List the compounds provided in the question. For example, let's say we have HCO₃⁻, H₂O, OH⁻, and HC₂O₄⁻.

2. **Determine Acid-Base Pairs**:
- **HCO₃⁻**:
- If HCO₃⁻ acts as a base and accepts a proton (H⁺), it becomes H₂CO₃ (carbonic acid).
- If HCO₃⁻ loses a proton, it becomes CO₃²⁻ (carbonate ion).
- Therefore, HCO₃⁻ can be paired with H₂CO₃ as a conjugate acid-base pair.

- **H₂O**:
- Water can act as an acid (donating H⁺) to become OH⁻ (hydroxide ion).
- Thus, H₂O and OH⁻ form a conjugate acid-base pair.

- **OH⁻**:
- If OH⁻ acts as a base and accepts a proton, it becomes H₂O.
- Therefore, OH⁻ and H₂O are also a conjugate acid-base pair.

- **HC₂O₄⁻**:
- If HC₂O₄⁻ loses a proton, it becomes C₂O₄²⁻ (oxalate ion).
- Thus, HC₂O₄⁻ and C₂O₄²⁻ can be considered a conjugate acid-base pair.

3. **Check for Conjugate Pairs**:
- Review each pair identified:
- HCO₃⁻ and H₂CO₃
- H₂O and OH⁻
- HC₂O₄⁻ and C₂O₄²⁻

4. **Conclusion**:
- The conjugate acid-base pairs identified are:
- HCO₃⁻ / H₂CO₃
- H₂O / OH⁻
- HC₂O₄⁻ / C₂O₄²⁻

### Final Answer:
The conjugate acid-base pairs are:
- HCO₃⁻ and H₂CO₃
- H₂O and OH⁻
- HC₂O₄⁻ and C₂O₄²⁻