Animated Solution for Chemistry - s and p-Block Elements: The compound that does not produce nitrogen gas by the thermal decomposition is

Thermal decomposition is like a chemical stress test. When we apply heat to a compound, we are essentially pumping energy into its bonds until they can no longer hold together. The way a compound breaks apart tells us a fascinating story about its internal structure and the stability of its constituent ions. In this problem, we are on a hunt to find the one compound that refuses to release nitrogen gas when subjected to this fiery trial.

Barium Azide

Let's begin with our first candidate, Barium Azide, ${\text{Ba(N}}_3{)}_2$. Azides are notorious in chemistry. The azide ion, ${\text{N}}_3^{-}$, is a high-energy, relatively unstable species. When you heat an alkali or alkaline earth metal azide, it doesn't just decompose; it shatters cleanly.

The reaction is beautifully simple:

This thermal decomposition is actually the preferred laboratory method for obtaining ultra-pure nitrogen gas, free from the noble gas impurities found in atmospheric nitrogen. So, Barium Azide is definitely a nitrogen producer.

Ammonium Dichromate

Next, we have Ammonium Dichromate, $({\text{NH}}_4{)}_2{\text{Cr}}_2{\text{O}}_7$. If you've ever witnessed the classic 'chemical volcano' demonstration, you know exactly what this compound does. It's a bright orange crystalline solid that, upon ignition, undergoes a spectacular intramolecular redox reaction.

Here is the chemical equation for the eruption:

In this reaction, the dichromate ion acts as a powerful oxidizing agent, oxidizing the nitrogen in the ammonium ion from an oxidation state of $-3$ to $0$ (elemental nitrogen). The chromium is reduced from $+6$ to $+3$, forming the fluffy green chromium(III) oxide that looks like volcanic ash. Once again, nitrogen gas is abundantly produced.

Our third option is Ammonium Nitrite, ${\text{NH}}_4{\text{NO}}_2$. This brings us to a crucial rule of thumb in inorganic chemistry: the thermal decomposition of an ammonium salt depends entirely on the nature of its anion.

If the anion is an oxidizing agent (like nitrite, nitrate, or dichromate), it will oxidize the ammonium ion, typically yielding nitrogen gas or nitrous oxide. Ammonium nitrite is the classic example used for the laboratory preparation of nitrogen:

The nitrite ion (${\text{NO}}_2^{-}$) oxidizes the ammonium ion (${\text{NH}}_4^{+}$), resulting in a clean release of nitrogen gas and water.

Ammonium Sulphate

Finally, we arrive at Ammonium Sulphate, $({\text{NH}}_4{)}_2{\text{SO}}_4$. Let's apply our rule of thumb here. Is the sulphate ion (${\text{SO}}_4^{2-}$) a strong oxidizing agent? No, it is not. It lacks the oxidizing power to strip electrons away from the nitrogen in the ammonium ion.

Because an intramolecular redox reaction cannot occur, the compound undergoes a simple thermal dissociation instead:

The heat simply provides enough energy to break the ionic lattice, driving off ammonia gas (${\text{NH}}_3$) and leaving behind sulphuric acid. No nitrogen gas is produced.

Therefore, by understanding the oxidizing power of the associated anions, we can confidently conclude that Ammonium Sulphate is the only compound among the choices that does not yield nitrogen gas upon thermal decomposition.