2KMnO4=MnO2+K2MnO4+O2m (KMnO4) = 12.8*98.75/10=12.64 гn (KMnO4) = m/M=12.64/158=0.08 мольn (O2) = 0.04 мольV (O2) = n*Vm=0.04*22.4=0.896 л