When acids react with active metals, they produce salt and hydrogen gas. The general equation for this reaction is:

$$Metal + Acid \rightarrow Salt + Hydrogen$$

For example, when hydrochloric acid (HCl) reacts with iron (Fe), it produces iron(II) chloride (FeCl2) and hydrogen gas (H2). The reaction is as follows:

$$Fe + 2HCl \rightarrow FeCl2 + H2$$

In this reaction, iron is the active metal, hydrochloric acid is the acid, iron(II) chloride is the salt, and hydrogen gas is the product.