[a123456]

A: Potassium Hydroxide + Sulfuric Acid -> Potassium Sulfate + Water
B: Copper Oxide + Sulfuric Acid -> Copper Sulfate + Water
C: Barium Nitrate + Sulfuric Acid -> Barium Sulfate + Nitric Acid
D: Zinc Carbonate + Sulfuric Acid -> Zinc Sulfate + Carbon Dioxide + Water

The answer provided was C. The only idea I have right now is that dilute acids dissociate partially. However, as seen, all the hydrogen ions of the sulfuric acid dissociate completely in the below reactions.

Thanks for the help.

[Orcio_87]

Did you heard about the law of dilution ? Dilution increases dissociation degree.

Maybe you should consider poor solubility of barium sulfate instead ?