Which nitrate will decompose to give `NO_(2)` on heating?

Options

A. `NaNO_(3)`
B. `KNO_(3)`
C. `RbNO_(3)`
D. `LiNO_(3)`

Explanation

To determine which nitrate will decompose to give \( NO_2 \) upon heating, we can follow these steps:

### Step 1: Understand the behavior of nitrates upon heating
Different nitrates decompose in different ways when heated. Generally, alkali metal nitrates decompose to produce nitrogen dioxide (\( NO_2 \)), oxygen (\( O_2 \)), and the corresponding metal oxide.

### Step 2: Identify the exceptional case of lithium nitrate
Among the alkali metal nitrates, lithium nitrate (\( LiNO_3 \)) behaves differently compared to the other alkali metal nitrates (sodium, potassium, rubidium, etc.).

### Step 3: Write the decomposition reaction for lithium nitrate
When lithium nitrate is heated, it decomposes as follows:
\[ 2 \, LiNO_3 \, \xrightarrow{\text{heat}} \, Li_2O + 2 \, NO_2 + O_2 \]
This reaction shows that lithium nitrate produces nitrogen dioxide (\( NO_2 \)) upon heating.

### Step 4: Compare with other alkali metal nitrates
In contrast, when sodium nitrate (\( NaNO_3 \)) is heated, it decomposes as follows:
\[ 2 \, NaNO_3 \, \xrightarrow{\text{heat}} \, 2 \, NaNO_2 + O_2 \]
This reaction produces oxygen (\( O_2 \)) instead of nitrogen dioxide.

### Step 5: Conclusion
From the above reactions, we can conclude that lithium nitrate (\( LiNO_3 \)) is the only nitrate that decomposes to give \( NO_2 \) upon heating, while the other alkali metal nitrates produce \( O_2 \).

### Final Answer
The nitrate that decomposes to give \( NO_2 \) on heating is \( LiNO_3 \).

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