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Fatty acid-soap systems exhibit a minimum in surface tension as a function of pH. What causes the increase in surface tension with decrease in pH below the pH of minimum surface tension? Increase in ionic repulsion in the adsorbed layer with decrease in pH reduces surfactant adsorption at the interface Unionized fatty acid that is present in this region is less surface active 0 Increase in the level of acid soap with decrease in pH results in increase surface tension Because of precipitation of unionized fatty acid in this region, the level of soluble surfactant decreases with decrease in pH