Sodium hydroxide will give the highest pH when equal volumes are dissolved because it is a strong base that dissociates completely to yield a high concentration of hydroxide ions. Magnesium hydroxide, although a base, is sparingly soluble so it produces far fewer OH⁻ ions in solution. Sulphuric acid is a strong acid and acetic acid is a weak acid; both produce H⁺ ions and lower pH values, so their solutions will be much less alkaline than NaOH commonly. Correct option – D.