Final answer:
Molecular nitrogen (N2) is generally un-reactive due to its strong triple bond between the nitrogen atoms, which is why it is the correct answer to the question.
Step-by-step explanation:
The question asks which nitrogen-containing substance is generally un-reactive. The correct answer to this question is a. N₂, which is molecular nitrogen, a diatomic molecule consisting of two nitrogen atoms triple-bonded to each other. Molecular nitrogen (N₂) is known for its inertness due to the strong triple bond between the nitrogen atoms, making it quite un-reactive under normal conditions.
Other nitrogen-containing substances such as NH₃ (ammonia), NaNO₂ (sodium nitrite), and NO (nitric oxide) are more reactive than molecular nitrogen.