Final answer:
Among the provided compounds, H₂SO₄ is the polyprotic acid as it can donate more than one proton in a stepwise manner. option a is correct.
Step-by-step explanation:
The polyprotic acid among the given compounds is H₂SO₄ (sulfuric acid). Polyprotic acids are capable of donating more than one proton (H+) in a solution, and this occurs in a stepwise manner.
H₂SO₄, being a strong acid and having two ionizable protons, does this sequentially; the first proton is lost easily resulting in a strong acid (HSO4−), and the second proton is lost less readily, leading to the formation of SO42− with increasing pKa value. In contrast, HCl is a strong monoprotic acid, and compounds like Mg(OH)2, NaBr, and KOH are bases, not acids.