Nitrogen is liberated by the thermal decomposition of only: (a) \(\mathrm{NH}_{4} \mathrm{NO}_{2}\) (b) \(\mathrm{NaN}_{3}\) (c) \(\left(\mathrm{NH}_{4}\right)_{2} \mathrm{Cr}_{2} \mathrm{O}_{7}\) (d) All the three

Thermal decomposition is a chemical reaction where a compound breaks down into simpler substances when heated. In this context, we are seeking a reaction that results in the liberation of nitrogen gas (N2).

We evaluate each compound to determine if it decomposes to release nitrogen gas when heated. (a) Ammonium nitrite ewline \begin{align*} \text{NH}_4\text{NO}_2 &\rightarrow N_2 + 2H_2O ewline \text{Decomposes to form N2 and water.} ewline \text{(b) Sodium azide} ewline \text{NaN}_3 &\rightarrow Na + N_2 ewline \text{Decomposes to form sodium and N2.} ewline \text{(c) Ammonium dichromate} ewline (\text{NH}_4)_2\text{Cr}_2\text{O}_7 &\rightarrow Cr_2\text{O}_3 + N_2 + 4H_2O ewline \text{Decomposes to form chromium(III) oxide, N2, and water.} ewline \text{All three compounds release nitrogen gas upon heating.} ewline \text{Thus, the correct answer is that all three liberate nitrogen gas.} ewline \text{Decomposes to form N2, sodium, and other decomposition products.} (c) Ammonium dichromate decomposes as follows: \[(\mathrm{NH}_4)_2\mathrm{Cr}_2\mathrm{O}_7 \rightarrow \mathrm{Cr}_2\mathrm{O}_3 + \mathrm{N}_2 + 4\mathrm{H}_2\mathrm{O}\]Decomposes to form nitrogen gas, chromium(III) oxide, and water vapor.