The `HF_(2)^(Θ)` ion solid state and in liquid `HF` but not in the dilute aqueous solution
In aqueous solution

Options

A. `HF` forms `H_(2)F^(o+)` and `overset(Θ)H,H_(2)O` being a stronger acid than `HF`
`H_(2)O+HFhArrH_(2)F^(o+)+Ooverset(Θ)H`
B. `HF` forms `H_(3)O^(o+)` and `F^(Θ) ,H_(2)O` being a weaker acid than `HF`
`H_(2)O + HF hArr H_(2)O^(o+) + F^(Θ)` .
C. H-bonding between `HF` and `H_(2)O` is observed
D. No change is observed

Answer

To solve the question regarding the behavior of the `HF2^-` ion in different states (solid, liquid, and dilute aqueous solution), we will analyze the properties of HF and its interactions in aqueous solution step by step.

### Step 1: Understanding the HF2^- Ion
The `HF2^-` ion exists in the solid state and in liquid HF. This ion is formed due to the hydrogen bonding between HF molecules. However, in dilute aqueous solutions, this ion does not exist.

**Hint:** Consider the nature of hydrogen bonding and the stability of ions in different states.

### Step 2: Behavior of HF in Aqueous Solution
HF is a weak acid compared to other hydrohalic acids like HCl, HBr, and HI. However, it is a stronger acid than water. When HF is dissolved in water, it partially dissociates to form hydronium ions (H3O^+) and fluoride ions (F^-).

**Hint:** Recall the definition of weak acids and how they dissociate in water.

### Step 3: The Reaction in Aqueous Solution
The dissociation of HF in water can be represented as:
\[ \text{HF} + \text{H}_2\text{O} \rightleftharpoons \text{H}_3\text{O}^+ + \text{F}^- \]
In this reaction, HF donates a proton (H^+) to water, forming H3O^+ and F^-.

**Hint:** Identify the products of the dissociation and the role of water in this reaction.

### Step 4: Comparing Conjugate Bases
The conjugate base of HF is F^-, and the conjugate base of water (H2O) is OH^-. Since OH^- is a stronger base than F^-, this indicates that HF is a stronger acid than water.

**Hint:** Consider the strength of conjugate bases when determining acid strength.

### Step 5: Conclusion about HF2^- in Aqueous Solution
In dilute aqueous solutions, the `HF2^-` ion does not exist because the equilibrium favors the formation of H3O^+ and F^- ions instead. Thus, in aqueous solution, HF primarily exists as H3O^+ and F^-.

**Hint:** Think about the stability of ions in solution and how equilibrium shifts in response to concentration changes.

### Final Answer
In aqueous solution, HF exists in the form of H3O^+ and F^-. Therefore, the correct option is:
**Option B: HF forms H3O^+ and F^-; H2O is a weaker acid compared to HF.**