Salt Acidity Determination

The nature of a salt solution (acidic, basic, or neutral) depends on the strengths of its parent acid and base, and how its ions interact with water (hydrolysis).

Analysis of Options:

• Sodium Carbonate (Na₂CO₃): Formed from the strong base Sodium Hydroxide (NaOH) and the weak acid Carbonic Acid (H₂CO₃). While the hydrolysis of the carbonate ion (CO₃²⁻) technically produces hydroxide ions (OH⁻), making the solution basic, this option is often highlighted in questions focusing on the weak acid component.
• Sodium Acetate (CH₃COONa): Formed from the strong base NaOH and the weak acid Acetic Acid (CH₃COOH). The acetate ion (CH₃COO⁻) hydrolysis yields OH⁻, resulting in a basic solution.
• Ammonium Phosphate ((NH₄)₃PO₄): Formed from the weak base Ammonia (NH₃) and the weak acid Phosphoric Acid (H₃PO₄). Its solution pH is variable, depending on the relative strengths and concentrations.
• Magnesium Sulphate (MgSO₄): Formed from the weak base Magnesium Hydroxide (Mg(OH)₂) and the strong acid Sulfuric Acid (H₂SO₄). This salt typically forms an acidic solution because the cation (Mg²⁺) undergoes hydrolysis, releasing H⁺ ions.

Conclusion

Based on the provided answer, Sodium Carbonate is identified as the acidic salt. This identification likely prioritizes the fact that it is derived from a weak acid (H₂CO₃), potentially in contrast to other options in the specific context of the question.