Solubility of Group 2 hydroxides increases down the group

Steps:

• Group 2 sulfates (MgSO₄, BaSO₄) are soluble or sparingly soluble but neutral, yielding pH near 7.
• Group 2 hydroxides produce basic solutions; Ba(OH)₂ solubility exceeds Mg(OH)₂, raising [OH⁻] more for Ba.
• pH 13.6 indicates strong base from highly soluble hydroxide (V = Ba(OH)₂).
• pH 9.4 indicates weaker base from less soluble hydroxide (W = Mg(OH)₂).

Why C is correct:

• Ba(OH)₂ dissolves more (Ksp ≈ 5×10⁻³) than Mg(OH)₂ (Ksp ≈ 6×10⁻¹²), producing higher [OH⁻] and pH for V.

Why the others are wrong:

• A: Sulfates form neutral solutions, not matching basic pH values.
• B: Sulfates swapped still neutral, ignoring observed basicity.
• D: Assigns less soluble Mg(OH)₂ to high-pH V, contradicting solubility trend.

Final answer: C