A compound which leaves behind no residue on heating is

Options

A. `Cu(NO_(3))_(2)`
B. `KNO_(3)`
C. `NH_(4)NO_(3)`
D. None of these

Answer

To determine a compound that leaves behind no residue upon heating, we will analyze the thermal decomposition of various compounds. The goal is to identify a compound that, when heated, produces only gaseous products and no solid residue.

### Step-by-Step Solution:

1. **Identify the Compounds**: We will consider the following compounds:
- Cu(NO3)2 (Copper(II) nitrate)
- KNO3 (Potassium nitrate)
- NH4NO3 (Ammonium nitrate)

2. **Analyze the Decomposition of Cu(NO3)2**:
- When heated, Cu(NO3)2 decomposes into:
\[ \text{Cu(NO}_3\text{)}_2 \rightarrow \text{CuO} + \text{2NO}_2 + \text{O}_2 \]
- Here, CuO is a solid residue. Therefore, Cu(NO3)2 does leave a residue.

**Hint**: Look for solid products in the decomposition reaction to determine if a residue is left.

3. **Analyze the Decomposition of KNO3**:
- When heated, KNO3 decomposes into:
\[ 2\text{KNO}_3 \rightarrow \text{K}_2\text{O} + \text{2N}_2 + \text{5O}_2 \]
- K2O is a solid residue. Thus, KNO3 also leaves a residue.

**Hint**: Check if the products include any solids; if they do, the compound leaves a residue.

4. **Analyze the Decomposition of NH4NO3**:
- When heated, NH4NO3 decomposes into:
\[ \text{NH}_4\text{NO}_3 \rightarrow \text{N}_2\text{O (g)} + 2\text{H}_2\text{O (g)} \]
- Both N2O and H2O are gases. Therefore, NH4NO3 does not leave any solid residue upon heating.

**Hint**: If all products are gaseous, then the compound does not leave a residue.

5. **Conclusion**:
- Among the compounds analyzed, only NH4NO3 decomposes to produce only gaseous products, leaving no residue behind upon heating.

Thus, the compound which leaves behind no residue on heating is **NH4NO3** (Ammonium nitrate).