Em tham khảo nha:

\(\begin{array}{l}
2KCl{O_3} \xrightarrow{t^0} 2KCl + 3{O_2}(1)\\
2KMn{O_4} \xrightarrow{t^0} {K_2}Mn{O_4} + Mn{O_2} + {O_2}(2)\\
{n_{KCl{O_3}}} = \dfrac{a}{{122,5}}\,mol \Rightarrow {n_{{O_2}(1)}} = \dfrac{a}{{122,5}} \times \dfrac{3}{2} = \dfrac{{3a}}{{245}}\,mol\\
{n_{KMn{O_4}}} = \dfrac{b}{{158}}\,mol \Rightarrow {n_{{O_2}(2)}} = \dfrac{b}{{158}} \times \frac{1}{2} = \frac{b}{{316}}\,mol\\
{n_{{O_2}(1)}} = {n_{{O_2}(2)}} \Rightarrow \dfrac{{3a}}{{245}} = \dfrac{b}{{316}}\\
 \Rightarrow \dfrac{a}{b} = \dfrac{{245}}{{3 \times 316}} = \dfrac{{245}}{{948}}
\end{array}\)