What is activity series ? How it helps in extraction of metals?

All the metals do not react with the same rate. Some react by fast, some react
moderately whereas others react very slowly. The series of metals in decreasing order of reactivity is called activity series.
K, Na, Ca, Mg, M Zn, Fe, Pb, Cu Ag, Au
High reactivity Moderate Reactivity Low reactivity
K, Na, Ca, Mg and Al simple chemical reduction methods like heating with C, CO to reduce the ores of these metals are not feasible. Zn, Fe, Pb, Cu the ores of these metals are generally present as sulphides or carbonates in nature. Sulphide ores are converted into oxides by heating them strongly in excess of air. The metal oxides are then reduced. Ag, Hg, Au are at the bottom of the activity series are often found in free state. Their reactivity with other atoms is very low. The oxides of these metals can be reduced to metals by heat alone and sometimes by dis-placement from their aqueous solutions.