When Borax is heated it forms a colourless glassy bead because of formation of :

Options

A. `B_(2)H_(6)`
B. `NaBO_(2)`
C. `B_(2)O_(3)`
D. `Na_(2)B_(4)O_(7)`

Explanation

**Step-by-Step Solution:**

1. **Identify the Composition of Borax**:
Borax is chemically represented as Na2B4O7·10H2O. It is a hydrated sodium borate.

2. **Heating Borax**:
When borax is heated, it undergoes a dehydration process where the water molecules are removed. This results in the formation of an anhydrous compound.

3. **Formation of Sodium Tetraborate**:
Upon heating, borax loses its water of crystallization and converts to sodium tetraborate (Na2B4O7).

4. **Further Heating**:
If the heating continues, sodium tetraborate can decompose to form sodium metaborate (NaBO2) and boron trioxide (B2O3). The reaction can be summarized as:
\[ Na2B4O7 \rightarrow 2 NaBO2 + B2O3 \]

5. **Formation of Glassy Bead**:
The combination of sodium metaborate (NaBO2) and boron trioxide (B2O3) results in a colorless glassy bead. This glassy bead is formed because of the melting and subsequent solidification of these compounds.

6. **Conclusion**:
Therefore, the formation of the colorless glassy bead when borax is heated is due to the formation of sodium metaborate (NaBO2) and boron trioxide (B2O3).

**Final Answer**: The correct option is that the colorless glassy bead is formed due to the formation of NaBO2 and B2O3.

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