Complete the following reaction and identify compounds `(A)` and `(B)`.
`B(OH)_(3)underset("Fusion")overset(NH_(4)HF_(2))to(A)underset(Delta)overset(B_(2)O_(3))to(B)`

Answer

To complete the reaction and identify the compounds (A) and (B), we can follow these steps:

### Step 1: Identify the Reactants
The reaction starts with boric acid, which has the formula \( B(OH)_3 \), and ammonium bifluoride, represented as \( NH_4HF_2 \).

### Step 2: Reaction of Boric Acid with Ammonium Bifluoride
When boric acid \( B(OH)_3 \) undergoes fusion with ammonium bifluoride \( NH_4HF_2 \), it forms ammonium tetrafluoroborate. The reaction can be represented as:
\[ B(OH)_3 + NH_4HF_2 \rightarrow NH_4BF_4 + H_2O \]
Here, \( NH_4BF_4 \) is the product formed, which we will denote as compound (A).

### Step 3: Reaction of Compound (A) with \( B_2O_3 \)
Next, compound (A) \( NH_4BF_4 \) reacts with \( B_2O_3 \) upon heating. The reaction can be represented as:
\[ NH_4BF_4 + B_2O_3 \rightarrow BF_3 + NH_3 + H_2O \]
In this reaction, boron trifluoride \( BF_3 \) is formed, which we will denote as compound (B).

### Step 4: Identify Compounds (A) and (B)
From the reactions above, we can identify:
- Compound (A) is \( NH_4BF_4 \) (ammonium tetrafluoroborate)
- Compound (B) is \( BF_3 \) (boron trifluoride)

### Final Answer
- Compound (A): \( NH_4BF_4 \)
- Compound (B): \( BF_3 \)

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