Basic oxides raise pH by forming hydroxides in water

Steps:

• Classify oxides: basic oxides form bases, acidic form acids, amphoteric or neutral show minimal reaction.
• Test reactivity: basic oxides like metal oxides dissolve to increase OH- ions, raising pH.
• Evaluate each option: MgO reacts to form base; others do not or form acids.
• Confirm: only basic, soluble oxides increase pH significantly.

Why A is correct:

• MgO is a basic oxide that reacts with water: MgO + H2O → Mg(OH)2, producing hydroxide ions to raise pH.

Why the others are wrong:

• B. Al2O3 is amphoteric and insoluble in water, causing no significant pH change.
• C. SiO2 is neutral and insoluble, with no reaction to alter pH.
• D. SO2 is an acidic oxide that forms sulfurous acid: SO2 + H2O → H2SO3, decreasing pH.

Final answer: A