\(n_{KMnO_4}=\dfrac{79}{158}=0.5\left(mol\right)\)
\(BTKL:\)
\(m_{O_2}=79-56.8=22.2\left(g\right)\)
\(n_{O_2}=\dfrac{22.2}{32}=0.69375\left(mol\right)\)
\(2KMnO_4\underrightarrow{^{t^0}}K_2MnO_4+MnO_2+O_2\)
\(1.3875....................................0.69375\)
\(H\%=\dfrac{0.5}{1.3875}\cdot100\%=36.04\%\)