The question is examining Module 5 Equilibrium and Acid Reactions, and in particular, solution equilibrium and dynamic equilibrium. The initial solution is saturated, no more solid can dissolve, so IV is wrong. The added mass of the radioactive solid will increase the total solids, so III is true. The solution will be radioactive due to the dynamic equilibrium between the new solid and the solvated ions, so II is true. It is debatable whether the extra radioactive solid has dissolved (due to dynamic equilibrium), so I could possibly be considered true. The best answer is (C) .