Amphoteric dissolution of Cu(OH)₂ requires excess base

Steps:

• Identify the reaction: Cu(OH)₂ reacts with water to form the tetrahydroxocuprate(II) ion, [Cu(OH)₄]²⁻, indicating amphoteric behavior.
• Balance the equation: Actual reaction is Cu(OH)₂ + 2OH⁻ → [Cu(OH)₄]²⁻, showing need for additional hydroxide ions beyond H₂O.
• Recall Cu(OH)₂ solubility: Insoluble in water alone but dissolves in strong base like NaOH to form the complex.
• Match to choices: Select the base that supplies OH⁻ ions.

Why D is correct:

• Sodium hydroxide (NaOH) provides excess OH⁻ ions, driving the formation of [Cu(OH)₄]²⁻ per the amphoteric dissolution formula.

Why the others are wrong:

• A. Catalase is an enzyme that decomposes H₂O₂, unrelated to metal hydroxide complexes.
• B. Copper sulfate (CuSO₄) is a copper source but not required for this specific hydroxide reaction.
• C. Hydrochloric acid (HCl) is an acid that reacts with Cu(OH)₂ to form soluble CuCl₂, not the basic complex.

Final answer: D