The strongest acid is:

Options

A. HF
B. `CH_(3)CO_(2)H`
C. `HF+SbF_(5)`
D. `H_(2)S`

Answer

To determine the strongest acid from the given options, we will analyze each compound based on their acidic strength.

### Step 1: Identify the Compounds
The compounds given are:
1. Hydrogen Fluoride (HF)
2. Acetic Acid (CH₃CO₂H)
3. Combination of HF and HPF₅
4. Hydrogen Sulfide (H₂S)

### Step 2: Analyze Each Compound
- **Hydrogen Fluoride (HF)**: HF is a weak acid. It does not dissociate completely in water, which limits its acidic strength.

- **Acetic Acid (CH₃CO₂H)**: Acetic acid is also a weak acid. Similar to HF, it does not fully dissociate in solution, making it weaker than strong acids like hydrochloric acid.

- **Combination of HF and HPF₅**: This combination leads to the formation of fluoroantimonic acid (HSBF₆) when reacted with SbF₅. Fluoroantimonic acid is known to be one of the strongest acids known, surpassing the strength of traditional strong acids.

- **Hydrogen Sulfide (H₂S)**: H₂S is a weak acid as well, and it does not compete with the strength of the acids mentioned above.

### Step 3: Conclusion
Based on the analysis, the strongest acid among the given options is the combination of HF and HPF₅, which forms fluoroantimonic acid. Therefore, the final answer is:

**The strongest acid is the combination of HF and HPF₅ (Option 3).**

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