Which of the following statements about `H_(3) BO_(3)` is not correct ?

Options

A. It has a layer structure in which planar `BO_(3)` units are joined by hydrogen bonds
B. It does not act as proton donor but acts as a Lewis acid by accepting hydroxyl ion
C. It is a strong tribasic acid
D. It is prepared by acidifying an aqueous solution of borax

Answer

To determine which statement about H₃BO₃ (boric acid) is not correct, we will evaluate each option provided in the question.

### Step-by-Step Solution:

1. **Evaluate Option 1**:
- The statement claims that H₃BO₃ has a layer structure in which planar BO₃ units are joined by hydrogen bonds.
- **Analysis**: Boric acid does indeed have a layered structure with planar BO₃ units. The BO₃ units are connected through hydrogen bonds, confirming this statement is correct.

2. **Evaluate Option 2**:
- The statement claims that H₃BO₃ does not act as a proton donor but acts as a Lewis acid by accepting hydroxyl ions.
- **Analysis**: Boric acid is known for its Lewis acid behavior, as it can accept hydroxyl ions (OH⁻) rather than donating protons (H⁺). This statement is also correct.

3. **Evaluate Option 3**:
- The statement claims that H₃BO₃ is a strong tribasic acid.
- **Analysis**: This statement is incorrect. Boric acid is a weak acid and is considered monobasic because it can only accept one hydroxyl ion (OH⁻) due to its electron deficiency and covalency of boron being 4. Therefore, it does not qualify as a tribasic acid.

4. **Evaluate Option 4**:
- The statement claims that H₃BO₃ is prepared by acidifying an aqueous solution of borax.
- **Analysis**: This statement is correct. Borax (Na₂B₄O₇) can be acidified with hydrochloric acid (HCl) to produce boric acid (H₃BO₃) along with sodium chloride (NaCl).

### Conclusion:
The statement that is not correct is **Option 3**, which claims that H₃BO₃ is a strong tribasic acid.

### Final Answer:
**Option 3 is not correct.**

---