Among the following the one which does not represent a conjugate acid-base pair is

Options

A. `HCl and Cl^(-)`
B. `HOH and OH^(-)`
C. `SO_(2)and H_(2)SO_(4)`
D. `NH_(4)^(+)and NH_(3)`

Answer

To determine which of the given options does not represent a conjugate acid-base pair, we need to understand the definitions of conjugate acids and bases:

1. **Conjugate Acid**: A species that can donate a proton (H⁺).
2. **Conjugate Base**: A species that can accept a proton (H⁺).

A conjugate acid-base pair consists of two species that differ by one proton.

Now, let's analyze each option provided in the question:

### Step 1: Analyze the first option - Cl⁻
- **Cl⁻** (chloride ion) can accept a proton to form **HCl** (hydrochloric acid).
- Thus, Cl⁻ is a conjugate base and HCl is its conjugate acid.
- This is a conjugate acid-base pair.

### Step 2: Analyze the second option - OH⁻
- **OH⁻** (hydroxide ion) can accept a proton to form **H₂O** (water).
- Thus, OH⁻ is a conjugate base and H₂O is its conjugate acid.
- This is also a conjugate acid-base pair.

### Step 3: Analyze the third option - H₂SO₄
- **H₂SO₄** (sulfuric acid) is already an acid and can donate a proton to form **HSO₄⁻** (hydrogen sulfate ion).
- However, H₂SO₄ does not act as a base in this context because it does not accept a proton to form another species.
- Therefore, H₂SO₄ does not represent a conjugate acid-base pair.

### Step 4: Analyze the fourth option - NH₄⁺ and NH₃
- **NH₄⁺** (ammonium ion) can donate a proton to form **NH₃** (ammonia).
- Thus, NH₄⁺ is a conjugate acid and NH₃ is its conjugate base.
- This is a conjugate acid-base pair.

### Conclusion
The option that does not represent a conjugate acid-base pair is **H₂SO₄**.

### Final Answer
The correct answer is **H₂SO₄** (option C).

---