To determine which nitrate will decompose to give nitrogen dioxide ( ) upon heating, let's first understand the thermal decomposition behavior of alkali metal nitrates.
Theoretical Explanation:
Nitrates of alkali metals (Group 1) typically decompose on heating to form different compounds. Here's what generally happens:
- For most alkali nitrates like sodium nitrate ( ), potassium nitrate ( ), and rubidium nitrate ( ), decomposition results in the formation of the metal nitrite and oxygen gas. The equation for sodium nitrate is as follows:
- However, lithium nitrate ( ) behaves differently due to the small size and high charge density of the lithium ion. On heating, it decomposes to produce lithium oxide ( ), nitrogen dioxide ( ), and oxygen gas. The decomposition of lithium nitrate is given by:
- This is because lithium exhibits properties somewhat similar to the alkaline earth metals, influencing its decomposition behavior.
Conclusion:
Given the options:
- : Does not produce upon decomposition.
- : Does not produce upon decomposition.
- : Does not produce upon decomposition.
- : Decomposes to produce .
The correct answer is LiNO₃ because it is the only nitrate among those listed that decomposes with the liberation of nitrogen dioxide.