For the reaction, $2{\mathrm{NO}}_2+\frac{1}{2}{\mathrm{O}}_2\stackrel{ }{\to }{\mathrm{N}}_2{\mathrm{O}}_5$  the rate of disappearance of NO₂ is  $6\times {10}^{-3}\mathrm{mole}.{\mathrm{lit}}^{-1}{\min }^{-1}.$ Rate of appearance of N₂O₅ will be

$$\begin{gathered} \mathrm{rate}=-\frac{1}{2}\frac{\mathrm{d}\left[{\mathrm{NO}}_2\right]}{\mathrm{dt}}=-2\frac{\mathrm{d}\left[{\mathrm{O}}_2\right]}{\mathrm{dt}}=+\frac{\mathrm{d}\left[{\mathrm{N}}_2{\mathrm{O}}_5\right]}{\mathrm{dt}} \\ \mathrm{given} -\frac{\mathrm{d}\left[{\mathrm{NO}}_2\right]}{\mathrm{dt}}=6\times {10}^{-3}\mathrm{mole} {\mathrm{lit}}^{-1}{\min }^{-1} \\ \frac{1}{2}\left(6\times {10}^{-3}\right)=+\frac{\mathrm{d}\left[{\mathrm{N}}_2{\mathrm{O}}_5\right]}{\mathrm{dt}} \\ +\frac{\mathrm{d}\left[{\mathrm{N}}_2{\mathrm{O}}_5\right]}{\mathrm{dt}}=3\times {10}^{-3}\mathrm{mole} {\mathrm{lit}}^{-1}{\min }^{-1} \\ +\frac{\mathrm{d}\left[{\mathrm{N}}_2{\mathrm{O}}_5\right]}{\mathrm{dt}}=\frac{3\times {10}^{-3}}{60}\mathrm{mole} {\mathrm{lit}}^{-1}{\mathrm{s}}^{-1} \\ +\frac{\mathrm{d}\left[{\mathrm{N}}_2{\mathrm{O}}_5\right]}{\mathrm{dt}}=5\times {10}^{-5}\mathrm{mole} {\mathrm{lit}}^{-1}{\mathrm{s}}^{-1} \end{gathered}$$