For a reaction A(g) $\to$ products,    the following data are available.

Initial pressure of $\mathrm{A},p_{\mathrm{A}}/\text{ Torr }$       429               273                     150

Half-life period, $t_{1/2^{/\mathrm{S}}}$                       350               550                      1001

The order of the reaction is

For zero-order reaction $t_{1/2}\propto [\mathrm{A}{]}_0$ For first-order reaction $t_{1/2}=\text{ constant }$

 For second-order reaction  $t_{1/2}\propto 1/[\mathrm{A}{]}_0$ For third-order reaction $t_{1/2}\propto 1/[\mathrm{A}{]}_0^2$

For the given data, $t_{1/2}[\mathrm{A}{]}_0$ is constant:

(429 Torr) (350 s) = 150 150 Torr s          (273 Torr) (550 s) = 150 150 Torr s

(150 Torr) (1001 s) = 150 150 Torr s 

Thus, the reaction is second order