Final answer:
In the described reaction, HCl is an acid as it donates a proton to water, making it a proton donor according to the Brønsted-Lowry Acid-Base Theory. So the correct option is A.
Step-by-step explanation:
In the given acid-base reaction, HCl is acting as an acid. When HCl (hydrogen chloride) is dissolved in water, it donates a proton (H+) to the water (H2O), which acts as a base, thus forming hydronium ions (H3O+) and chloride ions (Cl-). This process confirms that HCl is an acid according to the Brønsted-Lowry Acid-Base Theory, which defines an acid as a proton donor. Consequently, in the forward reaction of HCl ionizing in water, HCl is indeed the acid, not a conjugate acid nor a conjugate base.