The correct option is Barium sulphate.
Explanation
The reaction described is a classic example of a double displacement reaction (specifically a precipitation reaction), where there is an exchange of ions between the reactants.
Chemical Reaction Analysis:
- The reactants are aqueous solutions of Sodium Sulphate ($Na_2SO_4$) and Barium Chloride ($BaCl_2$).
- Upon mixing, the sulphate ions ($SO_4^{2-}$) from sodium sulphate displace the chloride ions ($Cl^-$) in barium chloride, and vice versa.
- The chemical equation for this reaction is:
$Na_2SO_4(aq) + BaCl_2(aq) \rightarrow BaSO_4(s) \downarrow + 2NaCl(aq)$
Identification of the Precipitate:
- Barium Sulphate ($BaSO_4$): This substance is insoluble in water and separates out as a solid. It forms a white precipitate immediately upon mixing.
- Sodium Chloride ($NaCl$): This remains dissolved in the solution and does not form a precipitate.
Key Takeaway:
In a double displacement reaction involving aqueous ionic compounds, if one of the products is insoluble in water, it forms a precipitate. The white precipitate formed by the reaction of sulphate salts with barium salts is Barium Sulphate.