`NO_(2)` gas evolves on thermal decomposition of which of the following compound(s)?

Options

A. `Hg(NO_(3))_(2)`
B. `KNO_(3)`
C. `N_(2)O_(4)`
D. `N_(2)O_(3)`

Explanation

To determine which compounds evolve NO₂ gas upon thermal decomposition, we will analyze each of the given compounds and their reactions when heated.

### Step-by-Step Solution:

1. **Identify the Compounds**: We have four compounds to consider:
- A) Hg(NO₃)₂ (Mercury(II) nitrate)
- B) KNO₃ (Potassium nitrate)
- C) N₂O₄ (Dinitrogen tetroxide)
- D) N₂O₃ (Dinitrogen trioxide)

2. **Thermal Decomposition of Hg(NO₃)₂**:
- When heated, mercury(II) nitrate decomposes as follows:
\[ \text{Hg(NO}_3\text{)}_2 \xrightarrow{\text{heat}} \text{HgO} + \text{NO}_2 + \text{O}_2 \]
- **Conclusion**: NO₂ gas is evolved.

3. **Thermal Decomposition of KNO₃**:
- When heated, potassium nitrate decomposes as follows:
\[ \text{KNO}_3 \xrightarrow{\text{heat}} \text{KNO}_2 + \text{O}_2 \]
- **Conclusion**: NO₂ gas is not evolved; only O₂ is produced.

4. **Thermal Decomposition of N₂O₄**:
- When heated, dinitrogen tetroxide decomposes as follows:
\[ \text{N}_2\text{O}_4 \xrightarrow{\text{heat}} 2\text{NO}_2 \]
- **Conclusion**: NO₂ gas is evolved.

5. **Thermal Decomposition of N₂O₃**:
- When heated, dinitrogen trioxide decomposes as follows:
\[ \text{N}_2\text{O}_3 \xrightarrow{\text{heat}} \text{NO} + \text{NO}_2 \]
- **Conclusion**: NO₂ gas is evolved.

### Final Answer:
The compounds that evolve NO₂ gas upon thermal decomposition are:
- A) Hg(NO₃)₂
- C) N₂O₄
- D) N₂O₃