Which of the following metal salts gives a red and opaque borax bead in the reducing flame (in cold)?

Options

A. `Ni`
B. `Fe`
C. `Cu`
D. `Mn`

Explanation

To determine which metal salt gives a red and opaque borax bead in a reducing flame, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Borax Bead Test**: The borax bead test involves heating borax (sodium tetraborate, Na2B4O7) to form a glassy bead. In a reducing flame, certain metal ions will impart specific colors and characteristics to the bead.

2. **Heating Borax**: When borax is heated, it decomposes to form sodium metaborate (NaBO2) and boron trioxide (B2O3). The borax bead can then be used to test for various metal ions.

3. **Identifying Metal Ions**: The color and opacity of the borax bead depend on the metal ion present. In this case, we are looking for a metal salt that gives a red and opaque bead.

4. **Analyzing the Options**: Among the given options, we need to identify which metal salt produces a red and opaque bead.

5. **Copper's Role**: Copper (Cu) is known to produce a red and opaque bead when heated in a reducing flame. This is due to the formation of copper(I) oxide (Cu2O), which imparts the red color.

6. **Conclusion**: Based on the analysis, the metal salt that gives a red and opaque borax bead in a reducing flame is copper.

### Final Answer:
The correct answer is **Copper (Cu)**.

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