The carbonate which does not leave a residue on heating is

Options

A. `Na_(2)CO_(3)`
B. `Ag_(2)CO_(3)`
C. `CuCO_(3)`
D. `(NH_(4))_(2)CO_(3)`

Answer

To determine which carbonate does not leave a residue upon heating, we will analyze the thermal decomposition of various carbonates.

### Step-by-Step Solution:

1. **Understanding Thermal Decomposition of Carbonates**:
Carbonates decompose upon heating to produce metal oxides (or other products) and carbon dioxide gas. The residue left after heating depends on the products formed.

2. **Analyzing Sodium Carbonate (Na2CO3)**:
- When heated, Na2CO3 decomposes as follows:
\[ \text{Na}_2\text{CO}_3 \rightarrow \text{Na}_2\text{O} + \text{CO}_2 \uparrow \]
- Here, sodium oxide (Na2O) is a solid residue that remains after heating. Thus, Na2CO3 leaves a residue.

3. **Analyzing Silver Carbonate (Ag2CO3)**:
- The decomposition reaction for Ag2CO3 is:
\[ \text{Ag}_2\text{CO}_3 \rightarrow 2\text{Ag} + \text{CO}_2 \uparrow + \frac{1}{2}\text{O}_2 \uparrow \]
- Silver (Ag) is a solid that remains after heating, indicating that Ag2CO3 also leaves a residue.

4. **Analyzing Calcium Carbonate (CaCO3)**:
- The decomposition reaction for CaCO3 is:
\[ \text{CaCO}_3 \rightarrow \text{CaO} + \text{CO}_2 \uparrow \]
- Calcium oxide (CaO) is a solid residue that remains after heating, meaning CaCO3 also leaves a residue.

5. **Analyzing Ammonium Carbonate (NH4CO3)**:
- The decomposition of NH4CO3 is as follows:
\[ \text{NH}_4\text{CO}_3 \rightarrow \text{NH}_3 \uparrow + \text{CO}_2 \uparrow + \text{H}_2\text{O} \uparrow \]
- Here, ammonia (NH3), carbon dioxide (CO2), and water (H2O) are all gases that escape upon heating. Therefore, NH4CO3 does not leave any residue.

6. **Conclusion**:
- Among the carbonates analyzed, the only one that does not leave a residue upon heating is **Ammonium Carbonate (NH4CO3)**.

### Final Answer:
The carbonate which does not leave a residue on heating is **NH4CO3**.