Borax Bead Test is carried out when the original mixture is coloured. It is done with the help of a cleam platinum wire on which a small loop is made at the end. When borax is heated on platinum wire loop transparent glass like bead is obtained. The hot bead is brought in contact with salt till it reacts with fused borax and colour is imparted to the bead. bead colour is noted.
`{:("Colour of the bead","Ion"),(1." Blue green",Cu^(2+)),(2." Yellow ",Fe^(3+)),(3." Green",Cr^(3+)),(4." Violet",Mn^(2+)),(5." Dark blue",Co^(2+)),(6." Brown",Ni^(2+)):}`
Q. Blue bead can be of:

Options

A. `Cu(BO_(2))_(2)`
B. `Co(BO_(2))_(2)`
C. both (a) and (b)
D. None of these

Answer

To determine which ion can produce a blue bead in the Borax bead test, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Borax Bead Test**: The Borax bead test is a qualitative analysis method used to identify metal ions based on the color of the bead formed when borax is heated and reacts with the metal ions.

2. **Preparation of the Bead**: A clean platinum wire is used to create a small loop at the end. This loop is dipped into borax (sodium tetraborate) and then heated in a flame until a transparent glass-like bead is formed.

3. **Coloring the Bead**: The hot bead is then brought into contact with a salt containing the metal ion of interest. The metal ion reacts with the borax to impart a specific color to the bead.

4. **Identifying the Blue Color**: According to the information provided, the color of the bead can indicate the presence of specific metal ions. The options given for the colors and corresponding ions include:
- Blue-green: Cu²⁺
- Yellow: Fe³⁺
- Green: Cr³⁺
- Violet: Mn²⁺
- Dark blue: Co²⁺
- Brown: Ni²⁺

5. **Determining the Ion for Blue Bead**: From the list, the ion that produces a blue color in the Borax bead test is Co²⁺ (cobalt ion), which gives a deep blue color when it reacts with borax to form cobalt metaborate (Co(BO₂)₂).

6. **Conclusion**: Therefore, the blue bead can be attributed to the presence of cobalt ions (Co²⁺).

### Final Answer:
The blue bead can be of Co²⁺ (cobalt ion).