Which statement is not correct about `H_3BO_3` ?

Options

A. It is a strong tribasic acid
B. It has a layer structure in which planar `BO_3` units are joined by hydrogen bonds
C. It is prepared by acidifying an aqueous solution of borax
D. It does not act as proton donor but acts as a Lewis acid by accepting hydroxyl ion

Answer

To determine which statement is not correct about H3BO3 (boric acid), we will analyze the properties and characteristics of H3BO3 step by step.

### Step-by-Step Solution:

1. **Understanding the Structure of H3BO3**:
- H3BO3 consists of a central boron atom (B) surrounded by three hydroxyl groups (OH). The structure can be represented as:
```
OH
|
OH - B - OH
```
- This indicates that boron is bonded to three oxygen atoms, each of which is further bonded to a hydrogen atom.

**Hint**: Remember that boron has a coordination number of 4, but in H3BO3, it forms three bonds with hydroxyl groups.

2. **Identifying the Acidic Nature**:
- H3BO3 is classified as a weak monobasic Lewis acid. This means it can accept hydroxyl ions (OH-) but does not donate protons (H+). The presence of three hydrogen atoms does not imply that it is tribasic.

**Hint**: Focus on the definition of Lewis acids and how they differ from Brønsted acids.

3. **Preparation of H3BO3**:
- H3BO3 can be prepared by acidifying borax (Na2B4O7) with sulfuric acid (H2SO4) in an aqueous solution. The reaction can be summarized as:
```
Na2B4O7 + H2SO4 + H2O → 4 H3BO3 + Na2SO4
```
- This confirms that H3BO3 is derived from borax through acidification.

**Hint**: Consider the reactants and products involved in the preparation of boric acid.

4. **Analyzing the Given Statements**:
- **Option A**: "It is a strong tribasic acid." - This statement is incorrect because H3BO3 is a weak monobasic Lewis acid.
- **Option B**: "It has a layer structure in which planar BO3 units are joined by hydrogen bonds." - This statement is correct.
- **Option C**: "It is prepared by acidifying an aqueous solution of borax." - This statement is correct.
- **Option D**: "It does not act as a proton donor but as a Lewis acid by accepting hydroxyl ions." - This statement is correct.

**Hint**: Carefully evaluate each statement against the properties and definitions discussed.

5. **Conclusion**:
- The statement that is not correct about H3BO3 is **Option A**: "It is a strong tribasic acid."

### Summary of the Incorrect Statement:
- The incorrect statement regarding H3BO3 is that it is a strong tribasic acid. In reality, it is a weak monobasic Lewis acid.