Answer: D (sulfuric acid). The question compares the number of ions released per mole when each substance is dissolved. Sulfuric acid is a strong acid that fully ionises, giving three ions per formula unit: \(\text{H}_2\text{SO}_4 \to 2\text{H}^+ + \text{SO}_4^{2-}\), so 1 mol gives 3 mol of ions. Sodium hydroxide is a strong base that fully ionises into two ions, Na⁺ and OH⁻, so 1 mol gives only 2 mol of ions.
Ethanoic acid is a weak acid that only partially ionises, so it releases relatively few ions. Ethanol is a covalent molecule that does not ionise at all, producing essentially no ions.
At the same 1 mol/dm³ concentration, sulfuric acid releases the greatest number of ions, so the answer is D.
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