Here's why:

* Acidic nature: Acids contain hydrogen ions (H⁺).

* Metal reactivity: Metals tend to lose electrons, becoming positively charged ions (cations).

* Reaction: When a metal reacts with an acid, the hydrogen ions from the acid gain electrons from the metal, forming neutral hydrogen atoms. These atoms then pair up to form hydrogen gas molecules (H₂).

Example:

Zinc metal reacts with hydrochloric acid (HCl) to produce zinc chloride (ZnCl₂) and hydrogen gas (H₂):

Zn(s) + 2HCl(aq) → ZnCl₂(aq) + H₂(g)

Note: Not all metals react with all acids. The reactivity of a metal depends on its position in the reactivity series. Metals above hydrogen in the reactivity series will react with acids to produce hydrogen gas.