Because 1. The gas released during heating can make the magenta solution fade, so there must be sulfurous acid in the solution.

2. After the alkali is adjusted to alkalinity, the gas released by heating can turn the wet red litmus paper blue, so there must be ammonium ions in the solution.

3. When chlorine water is added, the solution is slightly yellow, indicating that there must be bromine water in the solution.

The white precipitate is insoluble in dilute nitric acid, indicating that it is barium sulfate precipitate, but sulfurous acid is oxidized by chlorine water to generate sulfuric acid, and it is uncertain whether there are sulfate ions.