Laboratory methods :
(i) By heating chlorates, nitrates and permanganates.
Potassium chlorate in the presence of manganese dioxide on heating decomposes to form potassium chloride and oxygen.
(ii) By the thermal decomposition of metal oxides.
(iii) By the thermal decomposition of hydrogen peroxide : The thermal decomposition of hydrogen peroxide in the presence of finely divided metal and manganese dioxide used as catalyst gives oxygen.
