The reaction of a metal with an acid to produce a salt and hydrogen gas is a single displacement reaction.

Here's why:

* Single displacement reactions involve one element replacing another element in a compound.

* In this case, the metal (M) displaces the hydrogen (H) from the acid (HX) to form a salt (MX) and release hydrogen gas (H₂).

Here's a general equation representing this reaction:

M + HX → MX + H₂

Example:

* Zinc (Zn) reacts with hydrochloric acid (HCl) to produce zinc chloride (ZnCl₂) and hydrogen gas (H₂).

Zn + 2HCl → ZnCl₂ + H₂