The redox reaction between iodine I2 and thiosulfate S2O3^2- in the presence of hydrochloric acid HCl can be represented by the following equation:2 S2O3^2- aq + I2 aq S4O6^2- aq + 2 I^- aq When the pH of the solution decreases, the concentration of H+ ions increases due to the presence of hydrochloric acid. This increase in H+ ions can affect the equilibrium position of the redox reaction.In this reaction, iodine is reduced to iodide ions I^- , and thiosulfate ions are oxidized to tetrathionate ions S4O6^2- . The reaction is favored under acidic conditions, as the H+ ions help to stabilize the iodide ions I^- formed during the reaction.As the pH decreases i.e., the concentration of H+ ions increases , the equilibrium position of the redox reaction will shift to the right, favoring the formation of iodide ions I^- and tetrathionate ions S4O6^2- . This is because the increased concentration of H+ ions stabilizes the iodide ions, driving the reaction forward.In summary, decreasing the pH of the solution will shift the equilibrium position of the redox reaction between iodine and thiosulfate in the presence of hydrochloric acid to the right, favoring the formation of iodide ions and tetrathionate ions.