Group 2 solubility trends determine precipitates Steps: - Group 2 hydroxide solubility increases down the group: Mg(OH)₂ is insoluble (Ksp ≈ 5.6 × 10⁻¹²), forms precipitate; Ba(OH)₂ is soluble (Ksp ≈ 5 × 10⁻³), no precipitate. - Adding 0.1 mol dm⁻³ NaOH to 5 cm³ sample dilutes [OH⁻] to ≈0.016 mol dm⁻³; at equal [M²⁺], exceeds Ksp for Mg²⁺ but not Ba²⁺, so more precipitate with Mg²⁺ in Test 1. - Group 2 sulfate solubility decreases down the group: MgSO₄ is soluble, no precipitate; BaSO₄ is insoluble (Ksp ≈ 1.1 × 10⁻¹⁰), forms precipitate. - Adding 0.1 mol dm⁻³ Na₂SO₄ dilutes [SO₄²⁻] to ≈0.016 mol dm⁻³; exceeds Ksp for Ba²⁺ but MgSO₄ remains soluble, so more precipitate with Ba²⁺ in Test 2. Why C is correct: - Matches trends: Test 1 precipitate from less soluble Mg(OH)₂; Test 2 from less soluble BaSO₄. Why the others are wrong: - A: Reverses both; Ba²⁺ gives no hydroxide precipitate, little sulfate in Test 1 context. - B: Swaps Test 1; Ba(OH)₂ solubility prevents more precipitate there. - D: Reverses Test 2; MgSO₄ solubility …