In the reaction:
\[ \text{HCl} + \text{H}_2\text{O} \rightarrow \text{Cl}^- + \text{H}_3\text{O}^+ \]
HCl donates a proton (H+) to water (H2O), making HCl an acid and H3O+ the hydronium ion, which is the protonated form of water. The chloride ion (Cl-) is formed when HCl loses a proton, making it the conjugate base of HCl.
Thus, the correct statement is:
HCl is an acid, and Cl– is its conjugate base.