Explanation:
option A:
[tex]SO_{4}^{2-}[/tex] is an anion and [tex]Cl^{1-}[/tex] is also an anion.So,there is no reaction.
option B:
[tex]K^{+}[/tex] reacts with [tex]SO_{4}^{2-}[/tex] to form [tex]K_{2}SO_{4}[/tex].
Since [tex]K[/tex] is a first group element,all its salts are soluble in water.
Hence no precipitate is formed.
option C:
[tex]Na^{+}[/tex] reacts with [tex]SO_{4}^{2-}[/tex] to form [tex]Na_{2}SO_{4}[/tex].
Since [tex]Na[/tex] is a first group element,all its salts are soluble in water.
Hence no precipitate is formed.
option D:
[tex]Ba^{2+}[/tex] reacts with [tex]SO_{4}^{2-}[/tex] to form [tex]BaSO_{4}[/tex].
Solubility of sulphates of second group elements decrease down the group.
So,[tex]BaSO_{4}[/tex] is a precipitate.