Precipitation of Insoluble Barium Sulfate Steps:

• Identify barium sulfate (BaSO4) as an insoluble salt formed by double displacement reactions.
• Select routes involving soluble barium and sulfate salts to precipitate pure BaSO4.
• Ensure no side products contaminate the sample; filtration and washing yield purity.
• Verify route A uses BaCl2 + Na2SO4 → BaSO4 ↓ + 2NaCl, producing only insoluble BaSO4.

Why A is correct:

• Route A is a classic precipitation reaction yielding pure BaSO4 via metathesis, as BaSO4 has Ksp ≈ 1.1 × 10^-10, ensuring complete insolubility.

Why the others are wrong:

• B likely involves direct heating of barium carbonate, producing impurities like CO2 gas but not pure BaSO4.
• C may use sulfuric acid on barium metal, risking side reactions and soluble byproducts.
• D probably employs thermal decomposition, leading to mixed oxides instead of isolated BaSO4.

Not enough information on exact choices B, C, D.

Final answer: A