Oxides of highly active metals like potassium, sodium, calcium, magnesium and aluminium have great affinity towards oxygen and so cannot be reduced by carbon or carbon monoxide or hydrogen.
Metals in the middle of activity series (iron, zinc, lead, copper) are moderately reactive and are not found in oxide form. These are found in nature as sulphides or carbonate. These are first converted into oxides and can be reduced by C, CO or H2
ZnO + C + 400°c → Zn + CO
PbO + CO + heat → Pb + CO2
Metals low in the activity series is very less reactive and oxides of these metals are reduced to metals by heating alone.
