The potential of an electrode when each species involved in it exists in the standard state is called its standard potential. The standard reduction potential of a couple is the measure of its tendency to get reduced. A series obtained by arranging the various couples in order of their decreasing standard potensital is called electrochemical series. Any of the two couples of this series joined together gives an electrochemical cell in which reduction occurs at the electrode which occupiesthe higher position. The standard potential of hydrogen electrode is taken to be zero by convention. Given below are the sequence of half-reactions (acidic media) with relevant E^(@) values in volt at 298 K. MnO_(4)^(-)overset(0.50)rarr MnO_(4)^(2-)overset(2.26)rarr MnO_(2)overset(0.95)rarr Mn^(3+)overset(1.50)rarr Mn^(2+)overset(-1.18)rarr Mn Also given some more data are : Fe^(2+)overset(-0.44)rarr Fe_((s))overset(+0.036)rarr Fe^(3+) The value of E^(@) for the reaction is equal to MnO_(4)^(-)+5Fe^(2+)+8H^(+)rarr Mn^(2+)+5Fe^(3+)4H_(2)O,