In the following acid-base reaction, Cl- is the
HCI(g) + H2O(l) →H30+(aq) + Cl(aq)
acid
base
conjugate
base

conjugate base

Explanation:

The following equation is given in this question:

HCI(g) + H2O(l) → H30+(aq) + Cl-(aq)

In accordance to Brønsted–Lowry acid–base theory, an acid is a substance that loses an hydrogen ion (H+) or proton in an aqueous solution. This theory further indicated that the substance formed after an acid loses its hydrogen ion is called a CONJUGATE BASE.

In the above equation, HCl is the acid because it loses H+ while the substance formed after the loss of H+, which is Cl- is a conjugate base.