Which is incorrect ?

Options

A. Conjugate acid of `H_2O "is" H_3O^+`
B. Conjugate base of `HCO_3-"is" CO_3^(2-)`
C. Conjugate base of `NH_3 "is " NH_2^(Theta)`
D. Conjugate base of HOCI is `CI^-`

Answer

To determine which statement is incorrect regarding conjugate acids and bases, we will analyze each option step by step.

### Step-by-Step Solution:

1. **Understanding Conjugate Acid-Base Pairs**:
- An acid donates a proton (H⁺) and becomes its conjugate base.
- A base accepts a proton (H⁺) and becomes its conjugate acid.

2. **Analyzing the First Statement**:
- **Given**: H₂O as a base.
- **Action**: H₂O accepts H⁺ to form H₃O⁺.
- **Conclusion**: This is correct. H₃O⁺ is the conjugate acid of H₂O.

3. **Analyzing the Second Statement**:
- **Given**: HCO₃⁻ as an acid.
- **Action**: HCO₃⁻ loses H⁺ to form CO₃²⁻.
- **Conclusion**: This is correct. CO₃²⁻ is the conjugate base of HCO₃⁻.

4. **Analyzing the Third Statement**:
- **Given**: NH₃ as a base.
- **Action**: NH₃ loses H⁺ to form NH₂⁻.
- **Conclusion**: This is correct. NH₂⁻ is the conjugate base of NH₃.

5. **Analyzing the Fourth Statement**:
- **Given**: HOCl as an acid.
- **Action**: HOCl loses H⁺ to form OCl⁻.
- **Conclusion**: This is correct. OCl⁻ is the conjugate base of HOCl.
- However, the statement claims that the conjugate base is Cl⁻, which is incorrect.

### Final Conclusion:
- The incorrect statement is the one that claims the conjugate base of HOCl is Cl⁻ instead of OCl⁻. Therefore, the answer is option 4.