Final answer:
H₂SO₄ (sulfuric acid) is the strong acid among the substances listed, known for its complete ionization in water, while other options like HF, H₃PO₄, HSO₃⁻, and H₂CO₃ are weak acids.
Step-by-step explanation:
The strong acid among the substances listed is H₂SO₄ (sulfuric acid). Among the common strong acids are HCl, HBr, HI, HNO₃, HClO₄, and H₂SO₄. Strong acids are characterized by their complete ionization in water, releasing a proton (H+) and leaving no undissociated molecules in solution. This means H₂SO₄ dissociates completely into H+ and SO₄2- ions in aqueous solution. In contrast, HF (hydrofluoric acid), H₃PO₄ (phosphoric acid), HSO₃⁻ (hydrogensulfite ion), and H₂CO₃ (carbonic acid) are weak acids because they do not completely ionize in water.
For example, regarding the acid strength between H₂SO₄ and H₂SeO₄, both are oxyacids, and since sulfur has a higher electronegativity than selenium, H₂SO₄ is the stronger acid.