Answer: In the given reaction:
Cl⁻ + H₃O⁺ ⇋ H₂O⁻ + HCl
Acid: H₃O⁺ (hydronium ion)
Base: Cl⁻ (chloride ion)
Conjugate acid: H₂O⁻ (hydroxide ion)
Conjugate base: HCl (hydrochloric acid)
In this reaction, H₃O⁺ acts as an acid because it donates a proton (H⁺ ion) to Cl⁻, which acts as a base. After the proton transfer, H₃O⁺ becomes its conjugate base, H₂O⁻, and Cl⁻ becomes its conjugate acid, HCl.