Decreasing the pH of a solution containing iron III and ammonia means that the concentration of H+ ions in the solution is increasing. The formation of the complex ion Fe NH3 6^3+ can be represented by the following equation:Fe^3+ + 6NH3 Fe NH3 6^3+As the pH decreases, the concentration of NH3 ammonia will decrease because it reacts with the H+ ions to form NH4+ ammonium ions according to the following equation:NH3 + H+ NH4+As a result, the concentration of NH3 decreases, which in turn affects the equilibrium of the complex ion formation. According to Le Chatelier's principle, the equilibrium will shift to the left to counteract the decrease in NH3 concentration. This means that the formation of the complex ion Fe NH3 6^3+ will be less favored.However, it is important to note that the equilibrium constant K for the formation of the complex ion Fe NH3 6^3+ remains constant, as it is only dependent on temperature and not on the concentrations of the reactants or products. The shift in equilibrium due to the decrease in pH will affect the concentrations of the species involved, but the equilibrium constant itself will not change.