Provide the name of the oxyanion of the acid: H2CO3(aq).

H₂CO₃ is an oxyacid, which is the general name for the acids that contain oxygen, i.e. the chemical formula for an oxyacid contains hydrogen, a nonmetal, and oxygen: HₐXₓOₙ.

When an oxyacid ionizes it forms protons (H⁻) and oxyanions.

When H₂CO₃(aq) inonizes completely it does it according the equation:

H₂CO₃(aq) → 2 H⁺ (aq) + CO₃²⁻ (aq)

Meaning that it inoizes into two H⁺ cations and one CO₃²⁻ anion. The latter is the oxyanion.

Cations are positive ions. Anions are negative ions.

The name of H₂CO₃ is carbonic acid. From that you must know that the name of the oxyanion CO₃²⁻ is carbonate: the root ic from the acid changes to ate in the anion.

Summarizing:

Acid formula: H₂CO₃

Acid name : Carbonic acid

Oxyanion name : Carbonate

Oxyanion formula : CO₃²⁻

Additionally, you must know that when only one proton (instead of two) is released from the acid you form the ion HCO₃⁻ which is named bicarbonate or hydrogen carbonate.