Ans :- An electromotive force series (EMF series) is a metal's ranking in respect to inherent reactivity. Reactivity of metals. The metals located at the top of the series are considered the most noble, with the highest level of positive electrochemical potential.

1. The reactivity of the metaldepends on its tendency to lose electrons, i.e., tendency to form cation . This tendency depends on the magnitude of standard electrode potential. The metal which has lower value of standard electrode potential readily loses the electron or electrons and is form cations. Such a metal is said to be chemically reactive metal. The chemical reactivity of metals increases from top to bottom in the emf series. The metal higher in the emf series is more active than the metal lower in the series.For example :-Li+ + e has electrode potential of -3.05,Where as K+ + e has electrode potential of -2.93As Li has least value of electrode potential , therefore Li is more reactive.

2. Electropositive character of metals :The electropositive character also depends on the tendency to lose electron or electrons. The electropositive character of metals also increases from top to bottom in the emf series.On the basis of standard electrode potential values, metals are divided into three groups(a) Strongly electropositive metals :Metals having standard electrode potential near about – 2.0 volt or more negative .Like alkali metals, alkaline earth metals are strongly electropositive in nature.(b) Moderately electropositivemetals: Metals having values of electrode potentials between 0.0 and about – 2.0 volt are moderately electropositiveAl, Zn, Fe, Ni, Co, etc., belong to this group.(c) Weakly electropositive :The metals which are above hydrogen and possess positive values of electrode potentials are weakly electropositive metals.Cu, Hg, Ag, etc., belong to this group.

3. Displacement reactions(a) To predict whether a given metal will displace another, from its salt solution:A metal lower in the emf series will displace the metal from its solution which is higher in the emf series, i.e., The metal having high standard electrode potential will displace the metal from its salt’s solution which has lower value of standard electrode potential. A metal higher in the series has greater tendency to provide electrons to the cations of the metal to be precipitated.

(b) Displacement of one nonmetal from its salt solution by another non-metal:A non-metal having high value of reduction potential will displace another non-metal with lower reduction potential, electrons readily.

(c) Displacement of hydrogen from dilute acids by metals :The metal which can provide electrons to H+ ions present in dilute acids for reduction, evolve hydrogen from dilute acids.The metal having negative values of reduction potential possess the property of losing electron or electrons.Thus, the metals occupying bottom positions in the electrochemical series readily liberate hydrogen from dilute acids.The metals which are above hydrogen in electrochemical series like Cu, Hg, Au, Pt, etc., do not evolve hydrogen from dilute acids.

(d) Displacement of hydrogen from water :Iron and the metals below iron are capable of liberating hydrogen from water. The tendency increases from top to bottom in electrochemical series.Alkali and alkaline earth metals liberate hydrogen from cold water but Mg, Zn and Fe liberate hydrogen from hot water or steam.

4. Reducing power of metals:Reducing nature depends on the tendency of losing electrons. More the negative electrode potential, more is the tendency to lose electron or electrons. Thus reducing nature increases from top to bottom in the electrochemical series.Sodium is a stronger reducing agent than zincAlkali and alkaline earth metals are strong reducing agents.

(v) Oxidising nature of non-metals :Oxidising nature depends on the tendency to accept electron or electrons. higher the value of electrode potential, higher is the tendency to accept electrons. Thus, oxidising nature decreases from top to bottom in the electrochemical series.