The metal nitrate that liberates `NO_2` on heating

Options

A. `NaNO_3`
B. `LiNO_3`
C. `KNO_3`
D. `RbNO_3`

Explanation

To determine which metal nitrate liberates \( \text{NO}_2 \) upon heating, we will analyze the thermal decomposition of the given metal nitrates: \( \text{NaNO}_3 \), \( \text{LiNO}_3 \), \( \text{KNO}_3 \), and \( \text{RbNO}_3 \).

### Step-by-Step Solution:

1. **Understanding the Decomposition of Metal Nitrates**:
All metal nitrates decompose upon heating, but the products of this decomposition can vary depending on the metal involved.

2. **Analyzing Each Metal Nitrate**:
- **Sodium Nitrate (\( \text{NaNO}_3 \))**:
\[ 2 \text{NaNO}_3 \rightarrow 2 \text{NaNO}_2 + \text{O}_2 \]
- This reaction does not produce \( \text{NO}_2 \).

- **Lithium Nitrate (\( \text{LiNO}_3 \))**:
\[ 2 \text{LiNO}_3 \rightarrow \text{Li}_2\text{O} + 2 \text{NO}_2 + \text{O}_2 \]
- This reaction produces \( \text{NO}_2 \).

- **Potassium Nitrate (\( \text{KNO}_3 \))**:
\[ 2 \text{KNO}_3 \rightarrow 2 \text{KNO}_2 + \text{O}_2 \]
- This reaction does not produce \( \text{NO}_2 \).

- **Rubidium Nitrate (\( \text{RbNO}_3 \))**:
\[ 2 \text{RbNO}_3 \rightarrow 2 \text{RbNO}_2 + \text{O}_2 \]
- This reaction does not produce \( \text{NO}_2 \).

3. **Conclusion**:
From the analysis above, we find that only **Lithium Nitrate (\( \text{LiNO}_3 \))** liberates \( \text{NO}_2 \) upon heating.

### Final Answer:
The metal nitrate that liberates \( \text{NO}_2 \) on heating is **Lithium Nitrate (\( \text{LiNO}_3 \))**.

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