Assuming that a 3 percent solution represents a mass of solute in grams per volume of solution, there are 0.75 grams of KI in 25 mL of solution. However, the term percent solution is ambiguous; it can represent ratios of mass/mass, mass/volume or volume/volume.
If a 3 percent KI solution represents a mass over volume ratio in grams of solute per 100 mL solution, then the mass of KI in the solution is (3.0 grams KI / 100 mL solution) * 25 mL solution = 0.75 grams KI.
Using other definitions of a 3 percent solution, more information is needed to solve the problem. For example, if a 3 percent solution represents the ratio of mass of solute per total mass of the solution, then the density of the solution is first required to determine the mass of the solution in grams. Then, the number of grams of KI is 3 percent of the total mass of the solution.
If a 3 percent solution represents volume of solute in mL per total volume of solution in mL, then this means that there are 0.75 mL KI in the solution. In this case, the density of liquid KI would be required to convert 0.75 mL KI to the mass of KI in grams. However, KI is typically a solid salt. It has a melting point of 954 degrees Kelvin; therefore, it is unlikely that the context of this problem uses a volume/volume percentage.