In the reaction `HCl + H_(2)O to H_(3)^(+)O +Cl^(-)`

Options

A. `H_(2)O` is the conjugate base of HCl acid
B. `Cl^(-)` is the conjugate base of HCl acid
C. `Cl^(-)` is the conjugate acid of base
D. `H_(3)O^(+)` is the conjugate base of HCl

Explanation

To solve the problem regarding the reaction \( \text{HCl} + \text{H}_2\text{O} \rightarrow \text{H}_3\text{O}^+ + \text{Cl}^- \), we will analyze the roles of the substances involved according to the Bronsted-Lowry acid-base theory.

### Step-by-Step Solution:

1. **Identify the Reactants and Products**:
- The reactants are hydrochloric acid (HCl) and water (H₂O).
- The products are hydronium ion (H₃O⁺) and chloride ion (Cl⁻).

2. **Determine the Acid and Base**:
- According to the Bronsted-Lowry theory, an acid is a proton (H⁺) donor, and a base is a proton acceptor.
- In this reaction, HCl donates a proton (H⁺) to water. Therefore, HCl is acting as the acid.
- Water (H₂O) accepts the proton and is acting as the base.

3. **Identify the Conjugate Acid and Conjugate Base**:
- After donating a proton, HCl becomes Cl⁻, which is its conjugate base.
- After accepting a proton, H₂O becomes H₃O⁺, which is its conjugate acid.

4. **Conclusion**:
- From the reaction, we can conclude:
- HCl is the acid, and Cl⁻ is its conjugate base.
- H₂O is the base, and H₃O⁺ is its conjugate acid.

5. **Evaluate the Options**:
- Option 1: H₂O is the conjugate base of HCl. (Incorrect)
- Option 2: Cl⁻ is the conjugate base of HCl. (Correct)
- Option 3: Cl⁻ is the conjugate acid of H₂O. (Incorrect)
- Option 4: H₃O⁺ is the conjugate base of HCl. (Incorrect)

Thus, the correct answer is option 2: Cl⁻ is the conjugate base of HCl.