A compound of boron, A on heating swells up which on further heating forms glassy transparent mass `B`. The chemical constituent `B` is/are

Options

A. `Na_2 B_4 O_7` only
B. `NaBO_2` only
C. `NaBO_2 + B_2 O_3`
D. `Na_2 B_4 O_7 + B_2 O_3`

Answer

To solve the problem, we need to identify the compound A, which is a boron compound that swells upon heating and then transforms into a glassy transparent mass B upon further heating.

### Step-by-Step Solution:

1. **Identify Compound A**:
- The compound of boron that swells upon heating is borax, which has the chemical formula Na₂B₄O₇·10H₂O.

2. **Heating of Compound A**:
- When borax (Na₂B₄O₇·10H₂O) is heated, it loses its water molecules. The water of crystallization evaporates, causing the compound to swell and form a white solid, which is anhydrous borax (Na₂B₄O₇).

3. **Further Heating**:
- Upon further heating of the white mass (Na₂B₄O₇), it melts and transforms into a glassy transparent mass. This process results in the formation of sodium metaborate (NaBO₂) and boric anhydride (B₂O₃).

4. **Identify Chemical Constituents of B**:
- The glassy transparent mass B consists of sodium metaborate (NaBO₂) and boric anhydride (B₂O₃).

5. **Conclusion**:
- Therefore, the chemical constituents of the glassy transparent mass B are NaBO₂ and B₂O₃.

### Final Answer:
The chemical constituents of B are NaBO₂ plus B₂O₃.

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