What is the net ionic equation for the reaction between Na2SO4 and BaCl2 in aqueous solution, which forms a precipitate?

• A. Na2SO4 + BaCl2 -> BaSO4(s) + 2 NaCl
• B. BaSO4(s) + 2 Na+ + 2 Cl- -> Ba2+ + SO4^2- + 2 NaCl
• C. Ba2+ + SO4^2- -> BaSO4(s)
• D. Ba2+ + 2 Cl- -> BaCl2

Answer: (C)

When forming a net ionic equation, only the ions that actually change during the reaction are shown. Here, Na2SO4 and BaCl2 dissociate in water, giving Ba2+, SO4^2-, Na+, and Cl−. When mixed, Ba2+ and SO4^2− come together to form BaSO4, which is a solid and precipitates. The sodium and chloride ions stay dissolved as spectators and don’t participate in the solid-formation step, so they’re omitted in the net ionic equation. That leaves Ba2+ + SO4^2− → BaSO4(s). Other options either show the full ionic/formal equation with spectator ions, rearrange ions incorrectly, or describe the formation of BaCl2 instead of the precipitation that occurs.