Equilibrium analysis of Eu (III)- IBA/IPA/NAA system under thermodynamics conditions resulted in the composition of the system as 1:3 c mental-ligand; the resulting interaction surfaced as the chelation of metal with ligand with three primary and three secondary valencies. The successive lowering of stability of the systems in step-equlibria is ascribe the combined effect of statical, coulombic and steric factors. The stability and the thermodynamics of the systems involved are discussed. Varying opinions have been expressed on the mode of action of plant auxins, the controversy on this issue still hangs on Sawhney, Chauhan et.al. (1-4) studied some metal auxin system in solution and solid waste favouring chelation as a possible mode of action of plant auxins. This is an attempt on the analysing E(III) – Plant (IBA/IPA/NAA) systems under the thermodynamics conditions.

Keywords: Eu(III), Coulombic, Steric Factors, COOH, Spectrophotometrically.