Which is not true about borax?

Options

A. It is a useful primary standard for titrating against acids
B. One mole of borax contains 4 `B-O-B` bonds
C. Aqueous solution of borax can be used as buffer
D. It is made up of two triangular `BO_(3)` units and two tetrahedral `BO_(4)` units

Answer

To determine which statement about borax is not true, we need to analyze the properties and structure of borax, which is chemically represented as Na2B4O7·10H2O.

### Step-by-Step Solution:

1. **Identify the Chemical Formula**:
- The chemical formula of borax is Na2B4O7·10H2O. This indicates that it contains sodium (Na), boron (B), oxygen (O), and water (H2O).

2. **Understand the Structure**:
- Borax consists of boron-oxygen units. The structure can be described as containing two triangular BO3 units and two tetrahedral BO4 units. This is important for understanding its chemical behavior.

3. **Reactivity with Acids**:
- Borax is known to react with strong acids, such as hydrochloric acid (HCl). The reaction produces sodium chloride (NaCl), boric acid (H3BO3), and water (H2O). This indicates that borax can be used as a primary standard for titration against acids.

4. **Buffering Capacity**:
- An aqueous solution of borax can act as a buffer when combined with a strong base (like NaOH) and a weak acid (like H3BO3). This is due to the presence of borate ions, which can help maintain pH levels.

5. **Evaluate the Options**:
- Based on the above points, we can evaluate the statements provided in the question.
- If any statement contradicts the established facts about borax, that statement would be the one that is not true.

6. **Conclusion**:
- After analyzing the statements, it is found that one of the options is incorrect. This option does not align with the known properties and structure of borax.

### Final Answer:
The statement that is not true about borax is **Option 2**.