At $600 \mathrm{~K}, 2 \mathrm{~mol}$ of $\mathrm{NO}$ are mixed with $1 \mathrm{~mol}$ of $\mathrm{O}_{2}$.

$2 \mathrm{NO}_{(\mathrm{g})}+\mathrm{O}_{2}(\mathrm{g}) \rightleftarrows 2 \mathrm{NO}_{2}(\mathrm{g})$

The reaction occurring as above comes to equilibrium under a total pressure of 1 atm. Analysis of the system shows that $0.6 \mathrm{~mol}$ of oxygen are present at equilibrium. The equilibrium constant for the reaction is ________. (Nearest integer)