When a copper vessel is exposed to moist air for a long time, it acquires a dull green coating on its surface. The material of this green coating is a mixture of:

Options

A. Copper oxide and copper sulphate
B. Copper carbonate and copper hydroxide
C. Copper oxide and copper carbonate
D. Copper hydroxide and copper sulphate

Explanation

To solve the question regarding the dull green coating that forms on a copper vessel exposed to moist air, we can break down the process step by step.

### Step-by-Step Solution:

1. **Understanding the Reaction**: When copper is exposed to moist air, it undergoes a chemical reaction due to the presence of water vapor and carbon dioxide in the air.

2. **Formation of Copper Hydroxide**: The first reaction involves copper reacting with water. This reaction produces copper hydroxide (Cu(OH)₂).
- Reaction:
\[ \text{Cu} + \text{H}_2\text{O} \rightarrow \text{Cu(OH)}_2 \]

3. **Formation of Copper Carbonate**: The second reaction involves copper reacting with carbon dioxide (CO₂) present in the atmosphere. This reaction produces copper carbonate (CuCO₃).
- Reaction:
\[ \text{Cu} + \text{CO}_2 \rightarrow \text{CuCO}_3 \]

4. **Mixture of Compounds**: The dull green coating that forms on the copper vessel is a mixture of both copper hydroxide and copper carbonate. This mixture is often referred to as patina.

5. **Conclusion**: Therefore, the material of the green coating is a mixture of copper hydroxide (Cu(OH)₂) and copper carbonate (CuCO₃).

### Final Answer:
The material of the dull green coating is a mixture of copper hydroxide and copper carbonate.

---