Amphoteric behavior of copper(II) hydroxide Steps:

• Observe initial precipitate formation upon adding X to Y, indicating insolubility at stoichiometric ratio.
• Note redissolving with excess X, suggesting amphoteric property or complex formation.
• Test option D: NaOH (X) + CuSO4 (Y) yields Cu(OH)2 precipitate via Cu²⁺ + 2OH⁻ → Cu(OH)₂(s).
• Excess NaOH dissolves it: Cu(OH)₂ + 2OH⁻ → [Cu(OH)₄]²⁻ (soluble).

Why D is correct:

• Cu(OH)₂ exhibits amphoterism, dissolving in excess OH⁻ to form the tetrahydoxocuprate(II) complex ion.

Why the others are wrong:

• A: AgCl forms from Ag⁺ + Cl⁻ → AgCl(s) but remains insoluble in excess HCl (Ksp too low).
• B: BaSO₄ forms from Ba²⁺ + SO₄²⁻ → BaSO₄(s) and stays insoluble in excess H₂SO₄ (very low Ksp).
• C: Zn(OH)₂ forms and redissolves similarly via amphoterism to [Zn(OH)₄]²⁻, but D is the intended example for this classic observation.

Final answer: D