Final answer:
PbSO4 will be more soluble in an acidic solution than in pure water because the sulfate ion can react with hydrogen ions from the acid to form hydrogen sulfate, thereby increasing the solubility of PbSO4.
Step-by-step explanation:
The question asks us to determine which one of the following compounds is more soluble in an acidic solution than in water: CuS, AgCl, or PbSO4. The solubility of sparingly soluble salts in water can be affected by the presence of an acid due to the common ion effect or through the formation of a complex ion. In this case, PbSO4 would be more soluble in an acidic solution than in pure water.
This is because the sulfate ion (SO42-) can react with hydrogen ions (H+) from the acid to form hydrogen sulfate (HSO4-), which has a low tendency to precipitate. These hydrogen ions are plentiful in an acidic solution like HClO4. The reaction consuming sulfate ions shifts the equilibrium of PbSO4 dissolution to increase its solubility.