Group 2 oxides: increasing reactivity and basicity down the group

Steps:

• MgO reacts slowly with water, forming sparingly soluble Mg(OH)₂, so filtrate P is a dilute, weakly basic solution.
• BaO reacts readily with water, forming more soluble Ba(OH)₂, so filtrate Q is a concentrated, strongly basic solution.
• Reactivity increases down group 2, so BaO reacts more readily than MgO.
• Basicity strengthens down the group, so Q has higher pH (more alkaline) than P, making P the lower pH filtrate.

Why A is correct:

• BaO shows greater reactivity (faster reaction rate) per group 2 trend, and P has lower pH due to Mg(OH)₂'s weaker basicity and lower solubility.

Why the others are wrong:

• B: BaO reacts more readily, but Q has higher pH, not lower.
• C: MgO reacts less readily than BaO, so oxide is wrong.
• D: MgO reacts less readily, so oxide is wrong.

Final answer: A