Which chemical is used in the test for sulfate ions?

The test for sulfate ions involves the use of barium chloride. When barium chloride is added to a solution containing sulfate ions, a white precipitate of barium sulfate forms if sulfate is present. This reaction is a classic confirmatory test for sulfate ions and is based on the low solubility of barium sulfate in water.

Sodium hydroxide is often used in different tests, such as those for testing metal ions, but it does not specifically indicate the presence of sulfate ions. Similarly, silver nitrate is used to test for chloride ions, forming a white precipitate of silver chloride, and hydrochloric acid is primarily used in acid-base reactions and does not serve as a reagent for sulfate detection. The specific reaction of barium chloride with sulfate ions makes it the correct choice for identifying the presence of sulfate in a solution.