Neutral oxides do not react with water to change pH

Steps:

• Classify oxides by reactivity: acidic form H⁺ (lower pH), basic form OH⁻ (raise pH), neutral show no ion formation.
• Test Al₂O₃: amphoteric, hydrolyzes slightly to Al(OH)₃, producing OH⁻.
• Test SiO₂: inert, insoluble, no hydrolysis or ion release.
• Test P₂O₅: reacts to form H₃PO₄, releasing H⁺.

Why B is correct:

• SiO₂ is a neutral oxide; it does not react with water (SiO₂ + H₂O → no products), maintaining pH at 7 per oxide classification rules.

Why the others are wrong:

• A. Al₂O₃ hydrolyzes to Al(OH)₃, which dissociates slightly to raise pH (basic).
• C. P₂O₅ reacts as P₂O₅ + 3H₂O → 2H₃PO₄, an acid that lowers pH.

Final answer: B