So, , rder of reaction \(=1\)
\({t}_{1 / 2}=120 \mathrm{~min}\)
For \(90 \%\) completion of reactio
\(\Rightarrow \mathrm{k}=\frac{2.303}{\mathrm{t}} \log \left(\frac{\mathrm{a}}{\mathrm{a}-\mathrm{x}}\right)\)
\(\Rightarrow \frac{0.693}{\mathrm{t}_{1 / 2}}=\frac{2.303}{\mathrm{t}} \log \frac{100}{10}\)
\(\therefore \mathrm{t}=399 \mathrm{~min} .\)