If a pharmacist needs to dilute a solution from 10% to 5%, what action is needed?

To dilute a solution from 10% to 5%, the appropriate action is to add more solvent. A 10% solution means that there are 10 grams of solute in every 100 mL of solution. In order to bring the concentration down to 5%, you need to increase the volume of the total solution while keeping the amount of solute the same.

By adding more solvent, the same amount of solute is now spread out in a larger volume, effectively reducing the concentration of the solution to 5%. This method of dilution relies on the principle that concentration is inversely related to volume when the amount of solute remains constant.

Adding more solute would actually increase the concentration, while removing some solvent would concentrate the solution further, neither of which would achieve the goal of reducing the concentration to 5%. Therefore, the correct action in this scenario is indeed to add more solvent.