Here's why:

* Conjugate base: A conjugate base is formed when an acid loses a proton (H⁺).

* HSO₃⁻: This is the bisulfite ion, which can act as an acid.

* SO₃²⁻: This is the sulfite ion, formed when HSO₃⁻ loses a proton.

The reaction:

HSO₃⁻ (aq) ⇌ SO₃²⁻ (aq) + H⁺ (aq)