Water was taken in four beakers labelled as I to IV. In these beakers, the following substances were added.

Beaker I : Common salt

Beaker II : Alum

Beaker III : Potassium nitrate

Beaker IV : A few drops of barium chloride and a few drops of dil. ${\text{H}}_{\text{2}}{\text{SO}}_{\text{4}}$

After some time, the contents of the beakers were filtered. The contents of which beaker will leave residue on the filter paper?