$$\mathrm{r}=\mathrm{k}[\mathrm{A}]$$

So, order of reaction $$=1$$

$$\mathrm{t}_{1 / 2}=120 \mathrm{~min}$$

For $$90 \%$$ completion of reaction

$$\begin{aligned} & \Rightarrow \mathrm{k}=\frac{2.303}{\mathrm{t}} \log \left(\frac{\mathrm{a}}{\mathrm{a}-\mathrm{x}}\right) \\ & \Rightarrow \frac{0.693}{\mathrm{t}_{1 / 2}}=\frac{2.303}{\mathrm{t}} \log \frac{100}{10} \\ & \therefore \mathrm{t}=399 \mathrm{~min} . \end{aligned}$$