Borax bead test is given by:

Options

A. An aluminium salt
B. A cobalt salt
C. A copper `(II)` salt
D. A nickel salt

Answer

To solve the question about which salts give the borax bead test, we will analyze each option provided and determine if they show a color change when subjected to the borax bead test.

### Step-by-Step Solution:

1. **Understanding the Borax Bead Test**:
- The borax bead test is a qualitative test used to identify certain metal ions based on the color change of a borax bead when heated in a flame.
- The bead is made by mixing borax (sodium borate) with the metal salt and then heating it in a flame.

2. **Analyzing Each Salt**:
- **Aluminium Salt**:
- The transcript states that aluminium salt remains colorless when subjected to the borax bead test.
- **Conclusion**: Aluminium salt does not show a borax bead test.

- **Cobalt Salt**:
- The transcript mentions that cobalt salt shows a deep blue color in the borax bead test.
- **Conclusion**: Cobalt salt shows a borax bead test.

- **Copper(II) Salt**:
- According to the transcript, copper(II) salt shows a sky blue color in the oxidizing part and a red color in the reducing part of the borax bead test.
- **Conclusion**: Copper(II) salt shows a borax bead test.

- **Nickel Salt**:
- The transcript indicates that nickel salt shows a yellow-brown color in the oxidizing flame and a grey color in the reducing flame of the borax bead test.
- **Conclusion**: Nickel salt shows a borax bead test.

3. **Final Conclusion**:
- Based on the analysis:
- Aluminium salt: No borax bead test (colorless).
- Cobalt salt: Yes, shows borax bead test (deep blue).
- Copper(II) salt: Yes, shows borax bead test (sky blue and red).
- Nickel salt: Yes, shows borax bead test (yellow-brown and grey).
- Therefore, the correct answers are **B (Cobalt), C (Copper), and D (Nickel)**.

### Summary of the Correct Options:
- The salts that show the borax bead test are:
- Cobalt salt (B)
- Copper(II) salt (C)
- Nickel salt (D)