Dinitrogen and dioxygen are main constituents of air but these do not react with each other to form dioxides of nitrogen because ______.
| 1. | The reaction is endothermic and requires very high temperature |
| 2. | The reaction can be initiated only in presence of a catalyst |
| 3. | Oxides of nitrogen are unstable |
| 4. | N2 and O2 are unreactive |
