The correct answer is Precipitation reaction forming insoluble barium sulphate. Explanation & Key Takeaways: • When aqueous solutions of Barium chloride and Sodium sulphate are mixed, a chemical reaction occurs where the Barium ions (\( Ba^{2+} \)) from the barium chloride react with the Sulphate ions (\( SO_{4}^{2−} \)) from the sodium sulphate. • The balanced chemical equation for this process is: \( BaCl_{2}(aq) + Na_{2}SO_{4}(aq) \rightarrow BaSO_{4}(s) + 2NaCl(aq) \). • This reaction is specifically classified as a double displacement reaction because the positive and negative ions of the two ionic compounds exchange partners to form two new compounds. • The Barium sulphate (\( BaSO_{4} \)) produced is an insoluble salt that does not dissolve in water and settles out of the solution as a white, curd-like solid. • In chemistry, any reaction that produces an insoluble solid (precipitate) upon mixing two aqueous solutions is defined as a precipitation reaction. • The other product, Sodium chloride (\( NaCl \)), remains dissolved in the aqueous solution as it is highly soluble. Related Concepts: • Redox Reaction • Involves a change in oxidation states of atoms through the transfer of electrons. • In the reaction between barium chloride and sodium sulphate, the oxidation states of all elements remain constant; therefore, it is not a redox process. • Decomposition Reaction • A process where a single reactant breaks down into two or more simpler products, often requiring thermal energy, light, or electricity. • This scenario involves two distinct reactants forming two new products, which contradicts the definition of decomposition. • Evolution of Gas • Certain reactions result in the release of gaseous products like \( SO_{2} \) or \( CO_{2} \). • The mixing of these specific salt solutions does not involve any effervescence or the formation of Sulphur dioxide gas; the only visible change is the formation of a solid precipitate.