Precipitate Formation in Reactions

Steps:

• First mixture: Calcium reacts with water to form calcium hydroxide (white solid) and hydrogen gas.
• Second mixture: Calcium carbonate dissolves in hydrochloric acid, producing soluble calcium chloride, water, and carbon dioxide gas; no solid forms.
• Third mixture: Magnesium sulfate and barium nitrate undergo double displacement, yielding insoluble barium sulfate (white solid) and soluble magnesium nitrate.
• Total white solids: Two mixtures (first and third).

Why C is correct:

• Exactly two mixtures produce white solids, as Ca(OH)₂ and BaSO₄ are insoluble white precipitates per solubility rules.

Why the others are wrong:

• A: Fails to account for the two white solids formed.
• B: Misses the second white solid (BaSO₄).
• D: Includes the second mixture, which produces no solid.

Final answer: C