Question

Dinitrogen and dioxygen are main constituents of air, but these do not react with each other to form oxides of nitrogen because:
A. the reaction is endothermic and requires very high temperature.
B. the reaction can be initiated only in the presence of a catalyst.
C. oxides of nitrogen are unstable.
D. ${N}_{2}$ and ${O}_{2}$ are unreactive.

Answer 1

Hint: The reaction between dinitrogen and dioxygen is a chemical reaction which absorbs heat from its surrounding environment. Dissolving of ammonium chloride solvent in water or the melting of ice are examples of the same type of reaction.

Complete answer:
> Dinitrogen and dioxygen are the stable forms of nitrogen and oxygen atoms respectively.
Dinitrogen has a very high bond enthalpy. Due to this reason, it is practically inert at room temperature. However, the reactivity of dinitrogen increases as the temperature is increased.
On the other hand, dioxygen is a very reactive gas.
> As we know, the two main constituent gases of air are dinitrogen and dioxygen. Although being present in large amounts in air, they do not react with each other to form oxides of nitrogen. This is because dinitrogen has a triple bond between the two nitrogen atoms and for dinitrogen and dioxygen to react, this triple bond needs to be broken. But the bond dissociation energy that is the energy required to break the bond is very high for dinitrogen. This high amount of energy cannot be found in the atmosphere.
> Therefore, for this reaction to take place, it would require very high temperatures to generate enough energy to break the triple bond in dinitrogen. This reaction is also endothermic.

Hence, the correct answer is option (A).

Note: Students tend to confuse between options B and D. According to option (B), It says that a catalyst can only initiate this reaction but this reaction takes place only at high temperatures and does not require the presence of the catalyst. And according to option (D), it says that dinitrogen and dioxygen are unreactive but they do react with each other but this takes place only at a very high temperature.