Formation of insoluble barium sulfate precipitate

Steps:

• Group 2 elements include magnesium and barium; their compounds L and M must be soluble in water.
• Mixing soluble solutions forms a white precipitate, indicating an insoluble product from ion exchange.
• Test each option for solubility of both compounds and formation of a white insoluble Group 2 compound.
• Option A yields BaSO4, a white insoluble precipitate, while others do not.

Why A is correct:

• BaCl2 and MgSO4 are both soluble; mixing produces BaSO4 (insoluble white precipitate) and MgCl2 (soluble), per solubility rules for sulfates.

Why the others are wrong:

• B: BaSO4 is insoluble, so no aqueous solution of barium sulfate.
• C: Ba(NO3)2 and MgCl2 are soluble, but products BaCl2 and Mg(NO3)2 are all soluble—no precipitate.
• D: BaCO3 is insoluble, so no aqueous solution of barium carbonate.

Final answer: A