Oxide classification and reactivity with cold dilute NaOH

Steps:

• Classify oxides: Al₂O₃ (amphoteric), P₂O₅ and SO₂ (acidic), SiO₂ (weakly acidic).
• Recall that basic and amphoteric oxides react with NaOH to form salts; acidic oxides react if soluble or reactive under mild conditions.
• Test reactions: Al₂O₃ + NaOH → NaAlO₂; P₂O₅ + NaOH → Na₃PO₄; SO₂ + NaOH → Na₂SO₃; SiO₂ shows no significant reaction.
• Conclude SiO₂ does not react appreciably with cold dilute NaOH.

Why D is correct:

• SiO₂ is a weakly acidic, insoluble oxide that requires hot concentrated NaOH for reaction (SiO₂ + 2NaOH → Na₂SiO₃ + H₂O), not cold dilute conditions.

Why the others are wrong:

• A: Amphoteric Al₂O₃ reacts to form sodium aluminate (Al₂O₃ + 2NaOH → 2NaAlO₂ + H₂O).
• B: Acidic P₂O₅ reacts to form sodium phosphate (P₂O₅ + 6NaOH → 2Na₃PO₄ + 3H₂O).
• C: Acidic SO₂ reacts to form sodium sulfite (SO₂ + 2NaOH → Na₂SO₃ + H₂O).

Final answer: D