Precipitation Based on Solubility Rules

Steps:

• Apply solubility rules: most nitrates, sodium, and potassium salts are soluble; most sulfates are soluble except those of lead, barium, and strontium; chlorides are soluble except those of silver, lead, and mercury(I).
• Evaluate each compound: check if it dissolves in water or forms a solid precipitate.
• Identify the insoluble compound, as precipitation reactions form insoluble products from soluble reactants.
• Confirm the insoluble one matches a classic precipitation example.

Why D is correct:

• PbSO4 is insoluble per solubility rules (lead sulfate has low solubility, Ksp ≈ 1.6 × 10⁻⁸), so it precipitates from mixing soluble lead and sulfate salts.

Why the others are wrong:

• A. NaCl: All sodium salts are soluble, so NaCl dissolves fully.
• B. K2SO4: All potassium salts and most sulfates are soluble.
• C. Ca(NO3)2: All nitrates are soluble in water.

Final answer: D