Solubility difference enables filtration separation

Steps:

• Determine solubility of each component in water.
• Identify mixtures where one component dissolves and the other remains insoluble.
• Adding water and stirring dissolves the soluble component into solution.
• Filtering separates the insoluble solid from the solution containing the dissolved component.

Why A is correct:

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

Why the others are wrong:

• B: Both magnesium carbonate and iron are insoluble in water, so no dissolution occurs.
• C: Both sodium chloride and copper(II) sulfate are soluble in water, yielding a uniform solution.
• D: Both sulfuric acid and hydrochloric acid are fully miscible and soluble in water, forming a homogeneous mixture.

Final answer: A