Which of the following salt solutions will have a pH greater than 7?

Analyze the question: We need the salt whose aqueous solution is basic (pH > 7). This depends on the strong/weak nature of the acid and base that formed the salt.

Concept: Salt hydrolysis

• Strong acid + strong base → neutral solution (pH ≈ 7)
• Strong acid + weak base → acidic solution (pH < 7)
• Weak acid + strong base → basic solution (pH > 7)
• Acid salts of strong acids (e.g. NaHSO₄) behave as acidic because HSO₄⁻ releases H⁺.

Check each option:

• A. NaCl: from NaOH (strong base) and HCl (strong acid). Neutral, pH ≈ 7.
• B. NaHSO₄: HSO₄⁻ ionizes to give H⁺ and SO₄²⁻. Acidic, pH < 7.
• C. Na₂CO₄: this is probably a misprint of Na₂CO₃ (sodium carbonate), which comes from NaOH (strong base) and H₂CO₃ (weak acid). The carbonate ion hydrolyzes: CO₃²⁻ + H₂O ⇌ HCO₃⁻ + OH⁻. The OH⁻ released makes the solution basic, pH > 7.
• D. Na₂SO₄: from NaOH (strong base) and H₂SO₄ (strong acid). Neutral.
• E. MgCl₂: from Mg(OH)₂ (weak base) and HCl (strong acid). Mg²⁺ hydrolyzes slightly, so the solution is slightly acidic, pH < 7.

Note on the formula: "Na₂CO₄" is not a standard compound. It is almost certainly a typo for Na₂CO₃. Other options are neutral or acidic, so C is the only sensible choice.

Answer: C

Exam tip: Remember "the stronger partner wins." If the base is strong and the acid is weak, the solution is basic. Sodium carbonate, sodium ethanoate and sodium hydrogen carbonate are common basic salts in JAMB and NECO. Also, watch for acid salts like NaHSO₄, which are acidic.