Why the starch solution should be added after the reaction mixture becomes pale yellow and 65311?

The starch solution should be added after the reaction mixture becomes pale yellow because it serves as an indicator for the presence of iodine, which forms a dark blue complex with starch. If added too early, the starch may interfere with the reaction or give misleading results. Waiting until the mixture is pale yellow ensures that the reaction is sufficiently progressed to accurately determine the endpoint of the reaction. This timing allows for precise observations and measurements in experiments involving iodine.