Hydronium ion is formed by which of the following reaction?

Acid + water

The correct answer is option 1. Acid + water.

Hydrogen ions in HCl are produced in the presence of water.

The separation of H⁺ ion from HCl molecules cannot occur in the absence of water.

HCl + H₂O → H₃O⁺ + Cl^–

Hydrogen ions cannot exist alone, but they exist after combining with water molecules.

Thus, hydrogen ions must always be shown as H⁺(aq) or hydronium ion (H₃O⁺).

H⁺ + H₂O → H₃O⁺

Acids give H₃O⁺ or H⁺ (aq) ion in water.