For the reaction $2\mathrm{HI}_{(g)} \rightarrow \mathrm{H}_2{}_{(g)} + \mathrm{I}_2{}_{(g)},$ the question asks for the order of the reaction from the given data.

For decomposition of HI, the experimentally observed rate law is: $\text{Rate} = k[\mathrm{HI}]^2$ which means the reaction is second order with respect to HI, and hence the overall order is: $2$

Conclusion

The order of the reaction is: $\boxed{2}$

Comparison with stored answer

Stored correct answer = 2, which matches our derived answer.