A sample of pure ${\mathrm{NO}}_2$ gas heated to 1000 K decomposes :
$2{\mathrm{NO}}_2\left(\mathrm{g}\right)\rightleftharpoons 2\mathrm{NO}\left(\mathrm{g}\right)+{\mathrm{O}}_2\left(\mathrm{g}\right)$
The equilibrium constant ${\mathrm{K}}_{\mathrm{P}}$ is 100 atm. Analysis shows that the partial pressure of ${\mathrm{O}}_2$ is 0.25 atm. at equilibrium. The partial pressure of ${\mathrm{NO}}_2$ at equilibrium is :