When borax bead containing a small amount of metal salt ws heated in reducing flame of bunsane burner, the colour of the bead after heating was blue . The metal presence in the salt would be

Options

A. Manganese
B. Nickel
C. Cobalt
D. Chromium

Answer

To determine the metal present in the salt when a borax bead containing a small amount of metal salt is heated in a reducing flame and turns blue, we can follow these steps:

### Step-by-Step Solution:

1. **Understand Borax Bead Composition**:
- The borax bead is primarily composed of sodium tetraborate (Na2B4O7.10H2O). When heated, it loses water and forms a transparent bead.

2. **Heating the Borax Bead**:
- Upon heating, the hydrated borax (Na2B4O7.10H2O) loses its water molecules, resulting in the formation of anhydrous sodium tetraborate (Na2B4O7).
- Further heating leads to the formation of boron oxide (B2O3) and sodium metaborate (NaBO2), resulting in a colorless or transparent bead.

3. **Interaction with Metal Salt**:
- When the transparent bead is exposed to a colored metal salt in a reducing flame, the boron oxide (B2O3) reacts with the metal ions present in the salt.

4. **Identifying the Color Change**:
- The question states that the bead turns blue after heating. This color change indicates the presence of a specific metal ion that imparts a blue color to the bead.

5. **Common Metal Ions and Their Colors**:
- Various metal ions can produce different colors when heated in a borax bead. For instance:
- Cobalt (Co) typically produces a blue color.
- Copper (Cu) can produce green or blue colors depending on the oxidation state.
- Nickel (Ni) can produce green colors.

6. **Conclusion**:
- Since the bead turned blue, the metal present in the salt is most likely cobalt (Co), as it is known to produce a blue color when heated in a borax bead.

### Final Answer:
The metal present in the salt is **Cobalt (Co)**.