Answer and explanation;
-Dinitrogen tetroxide is a dimer and a colorless toxic gas which results from the reaction between two nitrogen dioxide molecules (NO2) a process called dimerization.
-The Dimerization process occurs readily when there is high concentration of mixtures of NO2 or when NO2 condenses on surfaces or at very low temperatures.
The reaction is;
2 NO2(g) → N2O4 (g)