A green mass is formed in the charcoal cavity test when a colourless salt `(X)` is fused with cobalt nitrate. (X) may contain

Options

A. Aluminium
B. copper
C. Barium
D. Zinc

Explanation

To solve the question regarding the formation of a green mass when a colorless salt (X) is fused with cobalt nitrate in the charcoal cavity test, we will analyze the possible components of salt (X) and the reactions involved.

### Step-by-Step Solution:

1. **Identify the Colorless Salt (X)**:
The question states that the colorless salt (X) can contain aluminum, copper, barium, or zinc. We need to determine which of these metals, when fused with cobalt nitrate, will produce a green mass.

2. **Analyze Each Metal**:
- **Aluminum**: When aluminum is tested in the charcoal cavity, it typically forms a blue mass. Therefore, aluminum is not the correct choice.
- **Copper**: Copper, when subjected to the charcoal cavity test, produces a brown residue. Thus, copper is also not the correct choice.
- **Barium**: Barium does not produce any significant reaction in the charcoal cavity test, so it can be ruled out.
- **Zinc**: Zinc is a potential candidate. When zinc salts are tested, they can react with cobalt nitrate.

3. **Reactions Involved**:
- When zinc sulfate (ZnSO4) is fused with sodium carbonate (Na2CO3), zinc carbonate (ZnCO3) is formed.
- Zinc carbonate decomposes upon heating to form zinc oxide (ZnO) and carbon dioxide (CO2).
- Cobalt nitrate (Co(NO3)2) decomposes upon heating to form cobalt oxide (CoO), nitrogen dioxide (NO2), and oxygen (O2).
- The green mass is formed when cobalt oxide reacts with zinc oxide:
\[ \text{CoO} + \text{ZnO} \rightarrow \text{CoZnO2} \]
This compound, cobalt zinc oxide (CoZnO2), is green in color.

4. **Conclusion**:
Based on the analysis, the colorless salt (X) that can produce a green mass when fused with cobalt nitrate is zinc. Therefore, the correct answer is that (X) may contain zinc.

### Final Answer:
The colorless salt (X) may contain zinc.

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