Which one of the following nitrogen oxides may dimerize ?

Nitrogen dioxide (NO2) is a unique nitrogen oxide that contains an odd number of valence electrons, making it a paramagnetic radical. To achieve a stable electronic configuration, two NO2 molecules readily undergo dimerization to form dinitrogen tetroxide (N2O4) [2]. This process is a reversible chemical equilibrium: 2NO2 ⅄ N2O4. The dimerization is exothermic, meaning that at lower temperatures or higher pressures, the equilibrium shifts toward the colorless dimer, N2O4, while at higher temperatures, it shifts back toward the reddish-brown monomer, NO2. While other nitrogen oxides like nitric oxide (NO) can also form dimers (N2O2) under specific conditions, NO2 is the most prominent example in standard chemical contexts due to its well-characterized equilibrium with N2O4 [2]. Other options like N2O, N2O3, and N2O5 are already stable molecular or ionic forms and do not typically undergo further dimerization.

Sources

1. [1] https://wwwn.cdc.gov/tsp/mmg/mmgdetails.aspx?mmgid=394&toxid=69
2. [2] https://pubmed.ncbi.nlm.nih.gov/28390374/