Borax on heating with cobalt oxide forms a blue bead of

Options

A. `Co(BO_(2))_(2)`
B. `Co(BO_(2))`
C. `Co_(3)(BO_(3))_(2)`
D. `Na_(3)CO(BO_(3))_(2)`

Explanation

To solve the question regarding the formation of a blue bead when borax is heated with cobalt oxide, we can break it down into the following steps:

### Step-by-Step Solution:

1. **Understanding Borax**:
- Borax is chemically represented as Na2B4O7. It is a boron compound that, upon heating, undergoes a decomposition reaction.

2. **Decomposition of Borax**:
- When borax is heated, it decomposes to form sodium metaborate (NaBO2) and boric oxide (B2O3).
- The reaction can be written as:
\[ \text{Na}_2\text{B}_4\text{O}_7 \rightarrow \text{NaBO}_2 + \text{B}_2\text{O}_3 \]

3. **Reaction with Cobalt Oxide**:
- The boric oxide (B2O3) produced from the decomposition of borax reacts with cobalt oxide (CoO) when heated together.
- The cobalt oxide reacts with boric oxide to form cobalt metaborate.

4. **Formation of Cobalt Metaborate**:
- The reaction can be represented as:
\[ \text{B}_2\text{O}_3 + \text{CoO} \rightarrow \text{CoB}_2\text{O}_4 \]
- This compound, cobalt metaborate, is responsible for the blue color of the bead formed during the borax bead test.

5. **Conclusion**:
- Therefore, the blue bead formed when borax is heated with cobalt oxide is cobalt metaborate, which can be represented as:
\[ \text{CoB}_2\text{O}_4 \text{ or } \text{Co}_2\text{B}_2\text{O}_4 \text{ (cobalt metaborate)} \]

### Final Answer:
The blue bead formed is cobalt metaborate, represented as CoB2O4.

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