a,
$2KMnO_4\buildrel{{t^o}}\over\to K_2MnO_4+MnO_2+O_2$
$2KClO_3\buildrel{{t^o}}\over\to 2KCl+3O_2$
b,
Gọi x, y là số mol $KMnO_4$, $KClO_3$
$\Rightarrow 158x+122,5y=273,4$ (1)
$n_{O_2}=\dfrac{49,23}{22,4}=2,2 mol$
$\Rightarrow 0,5x+1,5y=2,2$ (2)
(1)(2)$\Rightarrow x=0,8; y=1,2$
$\%m_{KMnO_4}=\dfrac{0,8.158.100}{273,4}=46,23\%$
$\%m_{KClO_3}=53,77\%$