At $330^{\circ} \mathrm{C},$ the rate constant for the decomposition of $\mathrm{NO}_{2}$ is $0.775 \mathrm{~L} /(\mathrm{mol} \cdot \mathrm{s})$. If the reaction is second order, what is the concentration of $\mathrm{NO}_{2}$ after $2.5 \times 10^{2}$ seconds if the starting concentration was $0.050 M ?$ What is the halflife of this reaction under these conditions?