The half life period for catalytic decomposition of ${\mathrm{AB}}_3$ at 50 mm is found to be 4 hrs and at 100 mm it is 2 hrs. The order of reaction is :

The half life period for catalytic decomposition of ${\mathrm{AB}}_3$ at 50 mm is found to be 4 hrs and at 100 mm it is 2 hrs. Thus,

$\frac{50}{100}={\left(\frac{4}{2}\right)}^{1-n}$

$\begin{array}{l}{2}^{n-1}=2\\ n-1=1\\ n=2\end{array}$

Hence the order of reaction is 2.