Answer: C: Hydrogen chloride gas and water
Step-by-step explanation: Hydronium ions can be represented as H₃O⁺. It is formed by the reaction between hydrogen chloride (HCl) gas and water. When hydrogen chloride is dissolved in water, it reacts with water molecules which forms hydronium and chloride ions. The chemical formula for this reaction can be represented as:
HCl + H₂O --> H₃O + Cl⁻