Which of the following ions in solution would form a white precipitate when acidified barium nitrate solution is added to it?

The formation of a white precipitate when acidified barium nitrate solution is added to a solution containing certain anions is based on the solubility rules of barium salts. When barium nitrate is added to a solution containing sulfate ions, barium sulfate is formed. Barium sulfate is known to be poorly soluble in water, leading to a white precipitate.

In contrast, while chloride and iodide ions can react with barium compounds, the resulting barium salts (barium chloride and barium iodide) are soluble in water and do not precipitate out. The nitrate ion also does not precipitate with barium since barium nitrate itself is soluble. Therefore, of these ions, only the sulfate ion will lead to the formation of a white precipitate upon the addition of acidified barium nitrate solution. This illustrates the significance of solubility products and precipitation reactions in analytical chemistry.