Salt reactions with NaOH affect pH; with H₂SO₄ form precipitates based on solubility

Steps:

• Identify salts in W and X from diagram: W contains NH₄Cl (weak base cation), X contains NaCl (neutral).
• Adding NaOH to W liberates NH₃ gas, increasing [OH⁻] more than in X, so pH higher in W.
• Identify salts in Y and Z: Y contains BaCl₂, Z contains CaCl₂.
• Adding H₂SO₄ to Y forms BaSO₄ (Ksp very low, complete precipitation, 0.0025 mol), to Z forms CaSO₄ (Ksp higher, partial precipitation, less than 0.0025 mol), so greater mass in Y.

Why A is correct:

• A matches: NH₄⁺ in W yields higher pH via NH₃ evolution; Ba²⁺ in Y yields more BaSO₄ precipitate per solubility rules.

Why the others are wrong:

• B: pH higher in X (neutral, lower pH than W); precipitate in Z (less CaSO₄).
• C: precipitate in Y correct, but pH higher in X (wrong, W higher).
• D: pH higher in X (wrong); precipitate in Z (less mass).

Final answer: A