Colour of the bead in borax bead testis mainly due to the formation of

Options

A. metal oxides
B. boron oxide
C. metal metaborates
D. elemental boron.

Answer

To answer the question about the color of the bead in the borax bead test, we can break down the process step by step:

### Step 1: Understanding the Borax Bead Test
The borax bead test is a qualitative analysis method used to identify certain metal ions based on the color produced when they are heated with borax (sodium tetraborate).

**Hint:** The borax bead test involves heating borax with metal oxides to observe color changes.

### Step 2: Heating Borax
When borax (Na2B4O7·10H2O) is heated, it loses its water of crystallization and transforms into sodium metaborate (NaBO2) and boric anhydride (B2O3). The reaction can be summarized as follows:

\[ \text{Na}_2\text{B}_4\text{O}_7 \cdot 10\text{H}_2\text{O} \xrightarrow{\text{heat}} \text{NaBO}_2 + \text{B}_2\text{O}_3 \]

**Hint:** Heating borax leads to the formation of sodium metaborate and boric anhydride.

### Step 3: Interaction with Metal Oxides
When a metal oxide (e.g., cobalt oxide) is mixed with the heated borax, it reacts to form a metal borate. For example, cobalt oxide reacts with boric anhydride to produce cobalt metaborate (CoBO2).

**Hint:** The specific metal oxide used will influence the color of the resulting bead.

### Step 4: Color of the Bead
The color of the bead is primarily due to the formation of the metal metaborate. In the case of cobalt oxide, the resulting cobalt metaborate gives a blue color to the bead.

**Hint:** The color observed is characteristic of the specific metal borate formed during the reaction.

### Conclusion
Thus, the color of the bead in the borax bead test is mainly due to the formation of metal metaborate, specifically cobalt metaborate in the example discussed.

**Final Answer:** The color of the bead in the borax bead test is mainly due to the formation of metal metaborate.