* Hydrogen Sulfate Ion: The key to its acidity lies in the hydrogen sulfate ion (HSO₄⁻). This ion can donate a proton (H⁺) to a base, making it an acid.

* Hydrolysis: When sodium hydrogen sulfate dissolves in water, it undergoes hydrolysis:

* NaHSO₄ + H₂O ⇌ H₃O⁺ + SO₄²⁻ + Na⁺

* This reaction generates hydronium ions (H₃O⁺), which are responsible for the acidic nature of the solution.

Therefore, sodium hydrogen sulfate is classified as an acid.