When aqueous solutions of two salts are mixed, the third salt formed may appear as a solid precipitate or a clear solution depending upon the solubility of its ions. It is observed that all salts of Na, K, NH4 are soluble. All nitrates and bicarbonates are also soluble. All halides (chlorides, bromides, iodides) are soluble except those of Ag, Hg (I) and Pb. All sulphates are soluble except those of Ag, Ca, Ba and Pb. Which one among the following combinations of solutions will produce a solid precipitate?

When aqueous solutions of sodium sulphate (Na2SO4) and barium chloride (BaCl2) are mixed, a double displacement reaction occurs. According to the solubility rules, all sodium salts are soluble, and most chloride salts are soluble. However, while most sulphate salts are soluble, barium sulphate (BaSO4) is a notable exception. Consequently, when Ba2+ ions from barium chloride meet SO4 2- ions from sodium sulphate, they form an insoluble white precipitate of barium sulphate. In contrast, magnesium sulphate and barium bicarbonate (Option 2) would form magnesium bicarbonate and barium sulphate, but bicarbonates are generally soluble. Lithium iodide and barium chloride (Option 3) involve halides of alkali and alkaline earth metals, which remain soluble. Ammonium sulphate and potassium bromide (Option 4) involve NH4 and K salts, which are universally soluble. Thus, only Option 1 produces a solid precipitate.