In the equilibrium `HClO_(4) + H_(2)O hArr H_(3)O^(+) + ClO_(4)^(-)`

Options

A. `HClO_(4)` is the conjugate acid of `H_(2)O`
B. `H_(2)O` is the conjugate acid of `H_(3)O^(+)`
C. `H_(3)O^(+)` is the conjugate base of `H_(2)O`
D. `ClO_(4)^(-)` is the conjugate base of `HCl_(4)`

Answer

To analyze the given equilibrium reaction:

\[ \text{HClO}_4 + \text{H}_2\text{O} \rightleftharpoons \text{H}_3\text{O}^+ + \text{ClO}_4^- \]

we need to identify the conjugate acids and bases involved in this reaction. Here’s a step-by-step breakdown of the solution:

### Step 1: Identify the Acid and Base
In the reaction, HClO4 (perchloric acid) donates a proton (H⁺) to water (H2O). Therefore, HClO4 acts as an acid, and H2O acts as a base.

**Hint:** Remember that an acid is a substance that donates protons, while a base is a substance that accepts protons.

### Step 2: Determine the Conjugate Base
When HClO4 donates a proton, it transforms into ClO4⁻ (perchlorate ion). This means that ClO4⁻ is the conjugate base of the acid HClO4.

**Hint:** The conjugate base is what remains after the acid has donated a proton.

### Step 3: Determine the Conjugate Acid
When H2O accepts a proton, it becomes H3O⁺ (hydronium ion). Therefore, H3O⁺ is the conjugate acid of the base H2O.

**Hint:** The conjugate acid is formed when a base accepts a proton.

### Step 4: Analyze the Options
Now we can analyze the statements given in the options:

1. **HClO4 is the conjugate acid of H2O.** - This statement is incorrect. HClO4 is the acid, while H3O⁺ is the conjugate acid of H2O.

2. **H2O is the conjugate acid of H3O⁺.** - This statement is incorrect. H3O⁺ is the conjugate acid of H2O, not the other way around.

3. **H3O⁺ is the conjugate base of H2O.** - This statement is incorrect. H3O⁺ is the conjugate acid of H2O.

4. **ClO4⁻ is the conjugate base of HClO4.** - This statement is correct. ClO4⁻ is indeed the conjugate base of HClO4.

### Conclusion
The correct statement is option 4: ClO4⁻ is the conjugate base of HClO4.

**Final Answer:** Option 4 is the correct option.