It was found that there was a linear correlation between the half-wave oxidation potentials E1/2 of the pentacyano (L) ferrates (II) complexes, where L refers to various substituted pyrazoles and indazoles, and pKaH+ of pyrazolium and indazolium cations respectively . In the present article the pKaH+ data of pyrazolium and indazolium cations is used to make Taft and Hammett plots and using the Taft * and Hammett  values the Reactivity-Selectivity Principle is explained in a simple and lucid way.