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

Options

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

Answer

To solve the question regarding the color of the bead in the borax bead test, we will follow these steps:

### Step 1: Understand the Borax Bead Test
The borax bead test is a qualitative analysis method used to identify certain metal ions based on the color of the bead formed when borax is heated with a metal salt.

**Hint:** Familiarize yourself with the purpose and procedure of the borax bead test.

### Step 2: Composition of Borax
Borax is chemically represented as Na₂B₄O₇·10H₂O. Upon heating, it loses its water of crystallization.

**Hint:** Remember the chemical formula of borax and what happens when it is heated.

### Step 3: Heating of Borax
When borax is strongly heated, it decomposes to form sodium metaborate (NaBO₂) and boric anhydride (B₂O₃).

**Hint:** Focus on the products formed during the heating process.

### Step 4: Formation of Beads
The heated borax forms a transparent glassy bead of sodium metaborate and boric anhydride. The boric anhydride is non-volatile and plays a crucial role in the formation of colored metaborates.

**Hint:** Understand the significance of the non-volatile nature of boric anhydride in the test.

### Step 5: Interaction with Metal Oxides
When a metal oxide (from a metal salt) interacts with boric anhydride, it forms metal metaborates. The color of the bead is determined by the specific metal metaborate formed.

**Hint:** Consider how different metal ions can affect the color of the bead.

### Step 6: Conclusion
The color of the bead in the borax bead test is mainly due to the formation of metal metaborates, which exhibit characteristic colors based on the metal present.

**Final Answer:** The correct option is **metal metaborates** (Option 3).