Matching salts to pure preparation methods Steps:

• Recall standard methods: soluble salts like sulfates and chlorides via acid-base reactions followed by crystallization; insoluble salts like silver chloride via precipitation and filtration.
• Check option A: copper(II) sulfate (CuO + H₂SO₄, crystallize), magnesium sulfate (Mg + H₂SO₄, crystallize), silver chloride (AgNO₃ + NaCl, precipitate), sodium chloride (NaOH + HCl titration, crystallize)—all yield pure samples.
• Eliminate B, C, D for mismatches or duplicates.
• Confirm A aligns with one method per salt for purity.

Why A is correct:

• Each salt uses a method ensuring purity: precipitation isolates insolubles (AgCl), while neutralization/crystallization purifies solubles (CuSO₄, MgSO₄, NaCl) per solubility rules.

Why the others are wrong:

• B: Lists silver chloride twice, duplicating an insoluble precipitation method.
• C: Includes only soluble salts, misassigning an insoluble precipitation method.
• D: Potassium sulfate mismatches a method suited for insolubles like silver chloride.

Final answer: A