Acidic and amphoteric oxides react with aqueous NaOH

Steps:

• Classify oxides: CaO and CuO are basic; ZnO is amphoteric; SO2 is acidic.
• Basic oxides react with acids but not bases like NaOH.
• Acidic oxides (SO2) react with NaOH to form salts (e.g., Na2SO3).
• Amphoteric oxides (ZnO) react with NaOH to form complex salts (e.g., Na2ZnO2).
• Identify pair where both are acidic or amphoteric.

Why D is correct:

• SO2 (acidic) + 2NaOH → Na2SO3 + H2O; ZnO (amphoteric) + 2NaOH → Na2ZnO2 + H2O.

Why the others are wrong:

• A: Both CaO and CuO are basic and do not react with NaOH.
• B: CaO is basic and does not react; only ZnO does.
• C: CuO is basic and does not react; only SO2 does.

Final answer: D