At 518 o C , the rate of decomposition of a sample of gaseous acetaldehyde, initially at a pressure of 363…

Rate$\propto {\left(\mathrm{concentration}\right)}^{\mathrm{n}}$

Let the initial concentration be $1 \mathrm{M}$.

According to the question,

$\begin{array}{cc}\mathrm{Concentration}& \mathrm{Rate}\\ 0.95 \mathrm{M}& 1\\ 0.67 \mathrm{M}& 0.5\end{array}$

Substituting in the general rate expression,

${\left(\frac{0.95}{0.67}\right)}^{\mathrm{n}}=\frac{1}{0.5}$

$\Rightarrow \mathrm{n}=2$