Solubility-based separation via dissolution and filtration

Steps:

• Determine solubility of each component in water.
• Add water and stir to dissolve soluble components.
• Filter to separate insoluble solids from the solution.
• Evaporate filtrate if needed to recover soluble components.

Why A is correct:

• Calcium carbonate is insoluble in water (sparingly soluble per solubility rules), while sodium chloride is highly soluble, allowing the carbonate to be filtered out as residue and chloride recovered from filtrate.

Why the others are wrong:

• B: Both magnesium and iron are insoluble metals; water dissolves neither, so no separation occurs.
• C: Both sodium chloride and copper(II) sulfate are soluble salts; everything dissolves, leaving no residue to filter.
• D: Both sulfuric and hydrochloric acids are miscible liquids; they form a homogeneous solution with no solid to filter.

Final answer: A