Chemical Kinetics

The rate constant for the reaction, $2 \mathrm{~N}_2 \mathrm{O}_{5(\mathrm{~g})} \rightarrow 2 \mathrm{~N}_2 \mathrm{O}_{4(\mathrm{~g})}+\mathrm{O}_{2(\mathrm{~g})}$ is $4.98 \times 10^{-4} \mathrm{~s}^{-1}$. What is the order of reaction?