The reaction of NO with ${\mathrm{N}}_2{\mathrm{O}}_4$ at 250K gives 

• Nitric oxide reacts with dinitrogen tetroxide at $250\mathrm{K}$ to produce dinitrogen trioxide

The following reaction takes place:

$2\mathrm{NO}\left(\mathrm{g}\right) +{\mathrm{N}}_2{\mathrm{O}}_4 \left(\mathrm{l}\right) \stackrel{250\mathrm{K}}{\to } {\mathrm{N}}_2{\mathrm{O}}_3\left(\mathrm{s}\right)$